We have investigated the expression of several growth-related genes in the liver after partial hepatectomy in three experimental models: normal, Dexamethasone-pretreated, and hypophysectomized rats. Dexamethasone and hypophysectomy resulted in a delay in the peak of cell replication in 6 and 18 h, respectively, when compared to the normal animals. TGF alpha mRNA expression was shifted together with the DNA synthesis, but the expression of c-myc, c-fos, c-jun, HGF, TGF beta 1, IL1 beta did not delay, This result suggests that liver-derived TGF alpha but not the other factors are important in the timing of the proliferative response after partial hepatectomy.