Statins are commonly prescribed cholesterol-lowering agents which inhibit the rate-limiting enzyme of the cholesterol biosynthetic pathway. In addition to inhibiting cholesterol synthesis, statins also inhibit the synthesis of other sterol and non-sterol compounds produced by the pathway including the isoprenoids, farnesyl (FP) and geranylgeranyl pyrophosphate (GGP). Certain proteins, most notably small GTP-binding proteins of the Ras superfamily, must be post-translationally modified by addition of a farnesyl or geranylgeranyl moiety in order to be properly targeted to membranes and to be active. Statins have been shown to affect cellular processes such as proliferation, signaling and apoptosis and it is likely that these effects are due, at least in part, to decreased isoprenoid synthesis. Certain statins have been shown to produce cataracts in experimental animals. We have previously demonstrated that lenses exposed to lovastatin during organ culture may develop cataracts as well, and we proposed that this resulted from decreased prenylation of small GTP-binding proteins. To test our hypothesis, rat lenses were exposed to lovastatin in organ culture with concomitant supplementation of the medium with GGP and/or FP. The results clearly demonstrated that GGP strongly inhibited lovastatin-induced lens opacification in this system while FP had little effect. GGP also markedly reduced the histological changes and the increased epithelial cell apoptosis induced in the cultured lenses by lovastatin. The data indicate that inhibition of protein prenylation, perhaps of Rho GTPases, is an important factor in the lovastatin-induced cataract in vitro.