The relationship between morphological changes in the liver during azo dye hepatocarcinogenesis in rats and cell proteins, especially alpha1-fetoprotein and alpha1-acid glycoprotein, was investigated by the immunofluorescence method. The isoelectric focusing fractionation was made to isolate alpha1-acid glycoprotein from normal rat plasma and to obtain a crude antigen containing alpha1-fetoprotein from rat amnionic fluid. The specific fluorescence of alpha1-fetoprotein was detected in the cytoplasm of the transitional cell and the cancer cell with rather a small ratio of cytoplasm/nucleus. The immunohistological study of alpha1-acid glycoprotein suggests that the intracellular concentration of the protein may decrease in the cytoplasm of hepatocytes in hyperplastic nocules, but may increase in the cytoplasm of bile duct cells, oval cells, transitional cells, and cancer cells. Based on these findings, a rational doubt is cast on the general assumption that the cancer cell originates from the hepatocyte in the hyperplastic nodule.