Content of high- and low-spin oxidized CYP was determined in liver microsomes and NDEA-induced hepatomas by method of optic spectrofotometry. Value of spin states ratio in hepatoma was shown to be greater then in liver. It in- creased under the action of inductors, which caused the syn- thesis of isoforms in high-spin configuration. Data obtained as a result of investigation of CYP isoform composition and metabolite phenotype of hepatoma have suggested that shift in balance of spin states in hepatoma was due to the decrease in the quantities of IIC11 and IIE1 isoforms as well as to the high level of IA1 isoform expression.