The effects of exogenous isoprenoids were investigated on A549 human lung adenocarcinoma cells. Among the tested isoprenoids, only farnesol and geranylgeraniol induce actin cytoskeleton disorganization, growth inhibition, and apoptosis. In contrast, desmosterol leads only to growth inhibition. We show that all tested isoprenoids are potent inhibitors of HMG CoA reductase activity, the sterols being the most powerful while they induce neither F-actin disorganization nor apoptosis. Thus the molecular mechanisms induced by farnesol and geranylgeraniol appear independent of reductase regulation. Our results point out the specific role of farnesol and geranylgeraniol on actin cytoskeleton organization and apoptosis in adenocarcinoma cells.