Mitomycin C. an antitumor drug. has been found to suppress the activities of the enzymes succinic dehydrogenase. glucose-6-phosphate dehydrogenase and A5-3/? hydroxysteroid dehydrogenase in the ovaries of sexually mature rats localized histochemically. The same treatment also produces an accumulation of cholesterol content with increased distribution of lipid granules. The DNA content of ovaries decreased. together with rise in DNase activity. Radioimmunoassay of gonadotrophic hormones of serum revealed a significant increase in FSH and LH content after the antibiotic treatment. The results indicate that the steroidogenic capacity of ovaries is reduced following Mitomycin C treatment possibly due to its direct effect on ovarian DNA content. The low level of circulating ovarian hormone stimulated the pituitary to increased synthesis of gonadotrophins.