Summary Primary hepatic carcinoma, without accompanying cirrhosis or fibrosis of the liver, was induced in rats with diethyl-nitrosamine. Hyperplastic nodules and nodular cytoplasmic alterations were found in the same livers. Autoradiographs after administration of tritiated thymidine showed no increase in DNA synthesis in morphologically normal areas or in foci of cytoplasmic alterations, but a striking increase in both hyperplastic nodules and carcinoma. It is concluded that primary hepatic carcinoma in the non-cirrhotic liver may arise through stages of increased nodular regeneration.