We examined the involvement of $p34^{cdc2}$ (maturation promoting factor catalytic subunit) and $pp60^{c-src}$ protein tyrosine kinases in regenerating rat liver. Maximum DNA synthesis reaches at 24 h after partial hepatectomy (PH) and 6 h later cell division starts (30 h after PH) [Bae, S. C. (1991) Ph. D. Dissertation, Seoul National University, 6-10]. $p34^{cdc2}$ was activated at 24 and 30.5 h after PH. These activations corresponded to the period of DNA synthesis and mitosis in regenerating rat liver. On the other hand, $pp60^{c-src}$ kinase was inactivated at first during preproliferation and S phase, however, reactivation occurred to the control level at 30.5 h after PH corresponding to the period of mitosis. These results suggest that both kinases are involved in the regeneration of rat liver.