Localization of characteristic precancerous lesions was compared with that of alpha-fetoprotein (alpha-FP) positive cells during hepatocarcinogenesis in Wistar rats fed 0.06% 3'-methyl-4-dimethylaminoazobenzene in basal diet. Proliferative activity of liver cells was simultaneously followed by deoxycytidylate deaminase. The first alpha-FP positive hepatocytes were found after 3 weeks of carcinogenesis in certain parts of the capsule 0.1--0.2 mm thick. In the seventh week of carcinogenesis their number increased and they were present in groups also subcapsularly. At this stage, hyperplastic islets began to be formed in the liver parenchyma. After 14 weeks of carcinogenesis, alpha-FP positive cell clusters and islets were also found in the deeper layers of liver parenchyma in regions with proliferation of transitory cells. Hyperplastic basophilic foci and islets occurred regularly, however, these were not identical with alpha-FP positive sites and their incidence was more frequent.