Cytochrome P-450 content measured spectrophotometrically 14 and 25 days after bilateral subdiaphragmal vagotomy in hepatocyte microsomes of inbred male rats was considerably reduced. The rate of aminopyrine demethylation and oxygen consumption decreased, while the duration of hexenal-induced sleep was prolonged. Monoxygenase responsible for p-hydroxylation of aniline proved relatively resistant to vagotomy.