Microsomal complexes of electron transfer were resistant to typical inhibitors of mitochondrial pathway of electron transport. In oxidation of NADP.H2 there were at least three point of molecular O2 reduction: NADP.H2-specific flavoprotein, Fe2+ participating in reactions of peroxidation of unsaturated fatty acids and cytochrome P-450. Efficiency of cytochrome P-450 inhibitors could not be evaluated by polarography as in the pathway several sites of molecular O2 activation were observed. In oxidation of NADP.H2 estimation of the rate of electron transfer reactions was carried out by monitoring of velocity of O2 absorption in presence of EDTA (inhibitor of the reaction of peroxidation) because about 50% of the total oxygen were utilized only in the process where NADP.H2 was oxidized. NAD.H2 oxidation, inhibited with EDTA, was activated by addition of Ca2+.