Hepatic cirrhosis produced by repeated inhalation of carbon tetrachloride is associated with reduced levels of microsomal cytochrome P450. In this study the C19-steroids androstenedione and testosterone were used as specific probes of the functional activity of several forms of cytochrome P450 in microsomal fractions from control and cirrhotic rat liver. The principal finding, that androstenedione 16 alpha-hydroxylation and testosterone 2 alpha-, 16 alpha-, and 17 alpha-hydroxylation were reduced to 14%-38% of control activity, strongly suggests that levels of the male sexually differentiated cytochrome P450 (P(450)16 alpha) are decreased in hepatic cirrhosis. The activity of other cytochrome P450-mediated C19-steroid hydroxylases, with the exception of androstenedione 6 beta-hydroxylase, appeared essentially unaltered in microsomes from cirrhotic rats. Cirrhosis induced by carbon tetrachloride was also associated with greatly decreased activity of the microsomal cytochrome P450-independent 17 beta-oxidoreductase, an enzyme that catalyzes the conversion of androstenedione to testosterone. Consequently, and in view of the impaired activity of cytochrome P450-mediated testosterone 17 alpha-hydroxylation, the capacity of cirrhotic microsomes to catalyze the interconversion of androstenedione and testosterone was much lower than that of control microsomes. The present data confirm and extend earlier observations that selective impairment of drug oxidation pathways occurs in hepatic cirrhosis. These changes are unrelated to the acute toxicity produced by carbon tetrachloride exposure. The available evidence supports the assertion that specific forms of cytochrome P450 are subject to altered regulation in cirrhosis.