Inhibitors of the enzyme that methylates ras proteins, the prenylated protein methyltransferase (PPMTase), are described. They are farnesyl derivatives of rigid carboxylic acids that recognize the farnesylcysteine recognition domain of the enzyme but do not serve as substrates. They also inhibit ras-dependent cell growth by a mechanism that is probably unrelated to inhibition of ras methylation, even though their potencies as PPMTase inhibitors and cell-growth inhibitors correlate well. The most potent inhibitor is S-trans,trans-farnesylthiosalicylic acid (FTS) (2). FTS (2) selectively inhibits the growth of human Ha-ras-transformed Rat1 cells in vitro (EC50 = 7.5 microM).