Exhibit 2 CERTIFICATE OF ADJUSTMENT Pursuant to Section 12 of the Rights Agreement (the "Rights Agreement"), dated as of June 24, 1997, between Schering-Plough Corporation (the "Company") and The Bank of New York, as Rights Agent, the Company hereby certifies as follows: At its September 22, 1998 meeting, the Company's Board of Directors declared a two-for-one division of the Company's Common Shares, par value $1 per share (the "Common Shares"), to be effected in the form of a 100% stock distribution (the "Distribu- tion") payable on December 2, 1998, to holders of record of the Common Shares at the close of business on November 6, 1998. The following adjustments shall be effected to reflect the Distribution as of December 2, 1998 pursuant to the terms of the Rights Agreement: (i) Number of Shares per Right. Pursuant to Section 11(n) of the Rights Agreement, each Right shall thereafter entitle the holder thereof to purchase one two-hundredth of a share of the Company's Series A Junior Participating Preferred Stock, par value $1 per share, upon proper exercise of such Right, subject to further adjustment in accordance with the terms of the Rights Agreement. (ii) Number of Rights. Pursuant to Section 11(n) of the Rights Agreement, one new Right will be issued with respect to each Common Share issued in the Distribution. Each Common Share certificate outstanding after the Distribution will represent the same number of Rights as Common Shares. (iii) Redemption Price. Pursuant to Section 23(a) of the Rights Agreement, the Redemption Price shall be adjusted from $.01 to $.005 per Right. Dated this 24th day of September, 1998. SCHERING-PLOUGH CORPORATION By:/s/ William J. Silbey William J. Silbey, Secretary