Inhibitory effects of 3-hydroxypyridines and of some drugs on NADPH-dependent lipid peroxidation was studied in liver microsomes of rats using a spectrophotometric technique with continuous monitoring of accumulation of peroxidation products. At the same time, inhibition of fatty acyl peroxidation catalyzed by the NADPH-dependent system and lipoxygenase from soybean was studied. The data obtained suggest that peroxidation, catalyzed by enzymes of two different types, may be inhibited to different degree by the same chemical compounds.