OBJECTIVE There is evidence to suggest that the release of neurohypophyseal hormones may be influenced by the circulating concentrations of gonadal steroids.We therefore monitored this relationship in women undergoing prophylactic bilateral oophorectomy at the time of hysterectomy with subsequent hormone replacement therapy and compared it with that in women undergoing hysterectomy with conservation of ovariesDESIGN Patients were randomly allocated to receive either transdermal oestradiol patches, 0.05 mg/day, or subdermal implants containing either 50 mg oestradiol or 50 mg oestradiol with 100 mg testosterone. Blood samples for determination of plasma hormone concentrations, electrolytes and osmolality were obtained immediately before and after surgery and then at two‐monthly intervals for 8 months and finally at 12 months.MEASUREMENTS Free oestradiol, vasopressin and oxytocin were measured by radioimmunoassay.RESULTS Vasopressin concentrations were found to fall after surgery in oophorectomized women, but not in those with ovaries. There were no changes in fluid balance to account for the reduced plasma vasopressin concentrations. During treatment oestradiol appeared to enhance and testosterone to suppress vasopressin release. Oophorectomy had no significant effect on plasma oxytocin concentrations, but in the groups receiving oestradiol implants concentrations fell significantly at 8 and 12 months compared with the value at 6 days.CONCLUSION The observed changes in plasma vasopressin concentrations were consistent with the observations in experimental animals and provide evidence that vasopressin release in the human is influenced