A study was performed to assess the effect of dilute vasopressin on intraoperative bleeding and intravasation of the medium during resectoscopic hysteroscopic surgery. Dilute vasopressin or placebo was injected into the cervical stroma at the commencement of resectoscopic endometrial ablation and/or submucous myomectomy in a prospective, computer-generated, double-blind, placebo study. The operator estimated the intraoperative bleeding. The inflow volume and outflow recovered volume of sorbitol, used as a distending medium, were recorded. Pressures were kept constant with a pump. Operating time was also recorded. In 64 women the mean inflow volume was 5,584 mL (range, 500-27,000), and the mean deficit (intravasation) was 311 mL (range, 0-2,100). The mean surgical time was 37.1 minutes (range, 11-120). The deficit volume was related to the duration of surgery (P = .001) and to total inflow volume (P = .001). Increased operating time and volume infused also increase intravasation. Multivariate analysis showed that patients receiving vasopressin had a 0.36 risk of intravasation (confidence limit, 0.14-0.91) as compared with the placebo. Vasopressin injected intracervically, in conjunction with resectoscopic intrauterine surgery, reduces but does not eliminate intravasation of the medium. It also decreases intraoperative bleeding.