Hyperprolactinaemia disrupts fertility in many species, perhaps by inhibiting ovarian follicular steroidogenesis. The present studies measured oestradiol and progesterone secretion from isolated follicles from rats rendered hyperprolactinaemic in one of two ways. Sustained hyperprolactinaemia was induced by transplantation of two donor pituitary grafts under the renal capsule of adult female rats; grafts remained in place for 3 months. Transient hyperprolactinaemia was induced by pseudopregnancy initiated by cervical stimulation. Small antral follicles were isolated from both groups of rats 8–10 days after the previous vaginal oestrous smear and also from a control group of dioestrous female rats. Follicles were incubated for 3 h in the presence or absence of human chorionic gonadotrophin (hCG) or testosterone. Basal and hCG-stimulated oestradiol production were each reduced in follicles from both hyperprolactinaemic groups, relative to follicles from dioestrous control rats. In contrast, in the presence of testosterone, all groups of follicles produced comparable amounts of oestradiol. hCG stimulated comparable progesterone production by follicles from all three treatment groups. Testosterone elicited smaller increases in progesterone accumulation by follicles from all in-vivo groups. Reduced basal and gonadotrophin-stimulated, but not androgen-stimulated, oestradiol accumulation suggests that androgen production rather than aromatase activity in small antral follicles may be impaired by long-term hyperprolactinaemia.