The relationship between morphological changes in the liver during azo dye hepatocarcinogenesis in rats and cell proteins, especially .alpha.1-fetoprotein and .alpha.1-acid glycoprotein, was investigated by the immunofluorescence method. Isoelectric focusing fractionation was done to isolate .alpha.1-acid glycoprotein from normal rat plasma and obtain a crude antigen containing .alpha.1-fetoprotein from rat amniotic fluid. The specific fluorescence of .alpha.1-fetoprotein was detected in the cytoplasm of transitional cells and cancer cells with a small ratio of cytoplasm/nucleus. The immunohistological study of .alpha.1-acid glycoprotein suggests that the intracellular concentration of the protein may decrease in the cytoplasm of hepatocytes in hyperplastic nodules, 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.