To estimate the efficacy of the vasopressin injection technique for laparoscopic cystectomy of ovarian endometriomas with regard to operative time and coagulation events. Prospective study (Canadian Task Force Classification II-1) Osaka Central Hospital in Osaka, Japan Fifteen women with single lobular similarly-sized ovarian endometrioma. Women who planned to undergo laparoscopic cystectomy of endometrioma were allocated randomly to 3 groups: (1) ordinary laparoscopic cystectomy without injection, (2) laparoscopic cystectomy with the injection of saline solution, and (3) laparoscopic cystectomy with the vasopressin injection technique. Reviewing the video, we counted the number of pinpoint bipolar coagulations on the normal ovarian cortex that were required from the beginning of stripping until hemostasis had been achieved, as well as the times required to achieve hemostasis. The group with the vasopressin injection technique required significantly fewer coagulation events (p=.041) to achieve hemostasis, as compared with the group receiving an ordinary cystectomy. The vasopressin injection technique reduces the use of coagulation, in such a way as to suggest the possibility to protect ovarian reserves.