The effect of denervation on △5-3β-hydroxysteroid dehydrogenase (3β-HSD) activity with pregnenolone as substrate was studied during pregnancy. The enzyme activity, that is interpreted as the capacity to secrete progesterone, was studied in both control and experimental pregnant rats. The ovaries of experimental rats were denervated 96 h prior to sacrifice. Denervation during early pregnancy did not affect 3β-HSD activity in the interstitial gland (IG) and corpus luteum (CL). However, denervation resulted in decreased activity in both the IG and CL on days 10, 14 and 18. This reduced activity is interpreted as a decreased capacity of denervated ovaries to synthesize progesterone at this time in pregn