In order to investigate the action of oncogenes in experimental hepatocarcinogenesis, the expression of c-myc, N-ras and H-ras were studied during early and late stages of DENA induced hepatocarcinogenesis in rats by using in situ hybridization. The results showed that overexpression of c-myc and N-ras was presented in teh proliferation hepatocytes and alternated hepatocytes foci during the early stage of hepatocarcinogenase, and with the formation and progression of hyperplastic hepatocytic nodules, the overexpresion cells of both were increased and often accompanied each other. Overexpression of H-ras appeared in the middle stage of hepatocarcinogenesis. The data obtained indicate that the abnormal expression of N-ras and c-myc in the hepatocarcinogenesis is not only an earlier molecule event which may relate to the initiation of HCC, but also the molecular basis for the morphogenesis of HCC, and these two functions took synergically. However, the abnormal expression of H-ras may have a promotive effect on the development of preneoplastic lesions, and also suggests that the malignant transformation of hepatocyte needs the cooperation of multiple oncogenes.