A long-acting LHRH agonist, Zoladex depot 3.6 mg, was administered as a monthly s.c. injection to seven premenopausal volunteers for a maximum of 6 months, starting in the luteal phase of the cycle. Transient stimulation of gonadotrophin release was observed 24 h after the initial depot, followed by sustained suppression of plasma LH, while FSH levels returned to the normal range. Plasma oestradiol concentrations fell to early follicular phase values within 14 d. Twice-weekly monitoring of urinary oestrone-3-glucuronide and pregnanediol demonstrated inhibition of ovulation and almost complete suppression of ovarian follicular activity throughout therapy. All the subjects became amenorrhoeic. Mean plasma testosterone concentrations were also significantly reduced while androstenedione remained within the pretreatment range. SHBG concentrations were not significantly reduced. After cessation of therapy, postovulatory menstruation occurred within 80 d of administration of the last depot.