Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARES

1. Identity of the issuer or the underlying issuer of existing shares to which voting rights are attached:

Abcam PLC

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

Yes

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

No

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

No

An event changing the breakdown of voting rights

No

Other (please specify):

No

3. Full name of person(s) subject to the notification obligation:

William Blair & Company, L.L.C.

4. Full name of shareholder(s) (if different from 3.):

5. Date of the transaction and date on which the threshold is crossed or reached:

January 20, 2011

6. Date on which issuer notified:

January 21, 2011

7. Threshold(s) that is/are crossed or reached:

Passed the 5% threshold

8. Notified details:

A: Voting rights attached to shares

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights

Direct

Direct

Indirect

Direct

Indirect

GB00B6774699

8,972,112

8,972,112

9,134,468

9,134,468

5.06%

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate

Exercise/ConversionPeriod

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

N/A

N/A

N/A

N/A

N/A

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Exerciseprice

Expirationdate

Exercise/Conversionperiod

Number of votingrights instrumentrefers to

% of voting rights

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

9,134,468

5.06%

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable:

 William Blair & Company, L.L.C., (William Blair) is an investment adviser registered under the U.S. Investment Advisers Act of 1940. As such, pursuant to advisory contracts, William Blair has the power to purchase and sell securities on behalf of its clients and the power to vote for most clients. Persons other than William Blair are entitled to receive all dividends from, and proceeds from the sale of all securities reported hereunder.

Proxy Voting:

10. Name of the proxy holder:

William Blair & Company, L.L.C.

11. Number of voting rights proxy holder will cease to hold:

N/A

12. Date on which proxy holder will cease to hold voting rights:

N/A

13. Additional information:

14. Contact name:

Walter R.Randall, Jr.

15. Contact telephone number:

+1 312 364 8720