Four isoenzymes of hexokinase were isolated by means of chromatography on DEAE-cellulose from soluble fraction of Vistar rat liver tissue. One of the isoenzymes (IV) was a glucokinase. Four fractions were also found in starch gel electrophoresis. These fractions catalyzed phosphorylation of glucose. Besides alterations in the total activity of hexokinase the changes in isoenzyme spectra were observed in carcinogenesis, caused by diethyl nitrosoamine. In the course of development of the blastomatose process in liver tissue content of isoenzymes I, II and, especially, of III was increased, and content of isoenzyme IV was decreased. In tissue of primary hepatomas, induced by diethyl nitrosoamine, the isoenzyme spectra of hexokinase did not significantly differ from the spectra of the enzyme in liver tissue at later stages of carcinogenesis.