During rat liver regeneration, at the onset of S-phase of the first cell cycle, an enhanced mevalonate incorporation into prenylated proteins is observed. The analysis of the lipid moieties of such proteins shows a 20-fold increased content of geraniol and farnesol. The expected increase of farnesylated and geranylgeranylated proteins in pre-S phase is confirmed by an increased level of lamin A, B, C and of several GTP-binding proteins. These results suggest a relevance of both farnesylation and geranylgeranylation in this phase of the cell cycle.