UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

o

Rule 13d-1(b)

x

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 744375205

1

Name of Reporting Person
Discovery Equity Partners, L.P.

2

Check the Appropriate Box if a Member of a Group (See Instructions)
Not Applicable

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
Illinois

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5

Sole Voting Power
None

6

Shared Voting Power
212,036

7

Sole Dispositive Power
None

8

Shared Dispositive Power
212,036

9

Aggregate Amount Beneficially Owned by Each Reporting Person
212,036

10

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11

Percent of Class Represented by Amount in Row (9)
4.1%

12

Type of Reporting Person (See Instructions)
PN

CUSIP No. 744375205

1

Name of Reporting Person
Discovery Group I, LLC

2

Check the Appropriate Box if a Member of a Group (See Instructions)
Not Applicable

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5

Sole Voting Power
None

6

Shared Voting Power
252,506

7

Sole Dispositive Power
None

8

Shared Dispositive Power
252,506

9

Aggregate Amount Beneficially Owned by Each Reporting Person
252,506

10

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11

Percent of Class Represented by Amount in Row (9)
4.8%

12

Type of Reporting Person (See Instructions)
OO

CUSIP No. 744375205

1

Name of Reporting Person
Daniel J. Donoghue

2

Check the Appropriate Box if a Member of a Group (See Instructions)
Not Applicable

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
U.S.A.

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5

Sole Voting Power
None

6

Shared Voting Power
252,506

7

Sole Dispositive Power
None

8

Shared Dispositive Power
252,506

9

Aggregate Amount Beneficially Owned by Each Reporting Person
252,506

10

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11

Percent of Class Represented by Amount in Row (9)
4.8%

12

Type of Reporting Person (See Instructions)
IN

CUSIP No. 744375205

1

Name of Reporting Person
Michael R. Murphy

2

Check the Appropriate Box if a Member of a Group (See Instructions)
Not Applicable

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
U.S.A.

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5

Sole Voting Power
None

6

Shared Voting Power
252,506

7

Sole Dispositive Power
None

8

Shared Dispositive Power
252,506

9

Aggregate Amount Beneficially Owned by Each Reporting Person
252,506

10

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11

Percent of Class Represented by Amount in Row (9)
4.8%

12

Type of Reporting Person (See Instructions)
IN

Item 1.

(a)

Name of Issuer:
Psychemedics Corporation

(b)

Address of Issuer’s Principal Executive Offices
125 Nagog Park, Acton, MA 01720

Item 2.

(a)

Name of Person Filing:
Discovery Equity Partners, L.P.  (“Discovery Partners”)

Discovery Group I, LLC, the general partner of Discovery Partners (“Discovery Group”)

Daniel J. Donoghue, a Managing Member of Discovery Group

Michael R. Murphy, a Managing Member of Discovery Group

(b)

Address of Principal Business Office or, if none, Residence:
Discovery Partners, Discovery Group, Mr. Donoghue, and Mr. Murphy are all located at:

191 North Wacker Drive, Suite 1685, Chicago, Illinois  60606

(c)

Citizenship:
Discovery Partners is an Illinois limited partnership

Discovery Group is a Delaware limited liability company

Mr. Donoghue and Mr. Murphy are U.S. citizens

(d)

Title of Class of Securities:
Common Stock, $.005 par value

(e)

CUSIP Number:
744375205

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
Not Applicable

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8);

(e)

o

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   
Discovery Partners – 212,036
Discovery Group – 252,506
Mr. Donoghue – 252,506
Mr. Murphy – 252,506

(b)

Percent of class:   
Discovery Partners – 4.1%
Discovery Group – 4.8%
Mr. Donoghue – 4.8%
Mr. Murphy – 4.8%

The foregoing percentages are based on 5,213,563 shares of Common Stock of the Issuer identified in Item 1 outstanding as of November 11, 2008, as reported in the Issuer’s Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2008.

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   
None

(ii)

Shared power to vote or to direct the vote    
Discovery Partners – 212,036
Discovery Group – 252,506
Mr. Donoghue – 252,506
Mr. Murphy – 252,506

(iii)

Sole power to dispose or to direct the disposition of   
None

(iv)

Shared power to dispose or to direct the disposition of   
Discovery Partners – 212,036
Discovery Group – 252,506
Mr. Donoghue – 252,506
Mr. Murphy – 252,506

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   x.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not Applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not Applicable

Item 8.

Identification and Classification of Members of the Group

Not Applicable

Item 9.

Notice of Dissolution of Group

Not Applicable

Item 10.

Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

February 13, 2009

Date

DISCOVERY GROUP I, LLC,

for itself and as general partner of

DISCOVERY EQUITY PARTNERS, L.P.

Michael R. Murphy*

Signature

Michael R. Murphy, Managing Member

Name/Title

Daniel J. Donoghue*

Signature

Daniel J. Donoghue

Name/Title

Michael R. Murphy*

Signature

Michael R. Murphy

Name/Title

*By: /s/ Mark Buckley

Mark Buckley

Attorney-in-Fact for Daniel J. Donoghue

Attorney-in-Fact for Michael R. Murphy