Maximal hepatic cytochrome P-450 levels were induced in the 17-day-old chick embryo (four to five times control) with a dose of sodium phenobarbital of 6 mg/egg/day for 2 days. Similar levels of hepatic cytochrome P-450 were induced with a dose of propylisopropylacetamide of 4 mg/egg/day for 1 day. Chick embryo hepatic microsomes from phenobarbital-pretreated or from untreated chick embryos could be stored for periods of 14 days at -70 degrees C without a decrease in cytochrome P-450 levels. Moreover, no significant differences was discerned between the degree of suicidal inactivation of chick embryo hepatic cytochrome P-450 by 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine in fresh and stored microsomes. Unlike rat hepatic microsomes, chick embryo hepatic microsomes do not undergo lipid peroxidative loss of cytochrome P-450 and heme when incubated in the presence of NADPH.