Lipid peroxidation was studied in dog and guinea pig adrenal cortex homogenates in vitro in presence of ascorbate, NADPH and I-(o-chlorophenyl)-I-(p-chlorophenyl)-2,2-dichloroethane (o,p'-DDD, chloditane) the substance exhibiting the specific impairing effect on human and dog adrenal gland cortex. The higher rate of spontaneous lipid peroxidation was detected in adrenal gland homogenates of guinea pig. NADPH inhibited accumulation of hydroperoxides in dog adrenal gland homogenates, while ascorbate-Fe2(+)-activated lipid peroxidation. Chloditane at concentrations 15.6 and 156 microM decreased the rate of spontaneous lipid peroxidation in dog adrenal gland homogenates and increased--in guinea pig preparations. Chloditane decreased distinctly the rate of lipid peroxidation in guinea pig adrenal gland homogenates, which was stimulated by ascorbate.