Abstract We have recently reported that extracts of the superior ovarian nerve (SON) of rats inhibit porcine theca cell androstenedione production. Theca cells obtained from prepubertal gilts were cultured under serum-free conditions for 48 h. The inhibitory effect of SON extracts occurred within 6 h of treatment, was irreversible and independent of the dose of luteinizing hormone (LH) employed. The SON extracts' actions were exerted at a site(s) distal to the generation of adenosine 3',5'-monophosphate (cyclic AMP), since they did not affect extracellular cyclic AMP accumulation, while causing a significant inhibition of androstenedione production. The SON extract decreased 17α-hydroxyprogesterone, androstenedione, testosterone, estradiol and estrone production while increasing progesterone and pregnenolone production, suggesting that the SON extract causes an inhibition of the 17α-hydroxylase:C 17–20 lyase complex. These results indicate that a factor(s) in the SON may play an important role in the regulation of follicular development, since thecal androgens are substrates for granulosa cell estrogen biosynthesis and are also involved in follicular atresia.