The influence of platinum derivatives, cisplatin (cis-diamminedichloroplatinum) and imidazolplatin (cis-diimidazoledichloroplatinum) on the activity of rat liver microsomal NADPH-oxidoreductases was investigated in vitro using spectrophotometrical and chemiluminometrical methods. In the range of concentrations from 1 to 12 µM cisplatin inhibited NADPH-cytochrome c-reductase activity and NADPH/lucigenin-dependent chemiluminescence of microsomes. The 3 µM cisplatin decreased the NADPH-dependent reductase activity by 50%. At concentrations less than 2,5 mM sanazole (drug AK-2123) did not prevent the inhibiting influence of cisplatin on microsomal NADPH-dependent reductases. Imidazolplatin insignificantly inhibited NADPH-reductases. It is concluded that negligible inhibiting effect of imidazolplatin on microsomal NADPH-oxidoreductase allows us to consider this platinum derivative as a promising compound for further experimental trials as anticancer drug with low toxic action on the normal tissues of an organism.