OBJECTIVE To investigate the role of the spleen on hepatocyte proliferative activity during experimental hepatocarcinogenesis in rats. METHODS Cell-cycle and expression of proliferating cell nuclear antigen (PCNA) of hepatocytes were studied by immunohistochemical and flow cytometric technique in two groups: splenectomy (45 rats) and sham-operation with laparotomy (45 rats). RESULTS (1) Hepatocirrhosis was formed in group A earlier than in group B. Marked degenerative changes of the liver parachyma showing vacuolization of hepatocytes were observed in hepatic lobules. (2) The proliferative level of hepatocytes increased with the progression of hepatocarcinogenesis, and topped at the 18 th week. (3) The proliferative level of the splenectomy group was lower than that of the sham-operation group in the mid-stage of carcinogenesis (t = 4.76, P < 0.05). After stopping feeding diethylnitrosamine (DENA), however, no difference was found in the hepatocyte proliferative activity between the two groups at the 18th week. CONCLUSIONS There is a close relationship between hepatic proliferative activity and spleen, and the spleen may play an important role in facilitating hepatic proliferation.