In order to investigate the production of eicosanoids in human endometrium, myometrium, leiomyoma, adenomyosis, normal ovary, non-endometrial cyst and endometrial cyst, slices of each tissue were incubated. 6-Keto-prostaglandin (PG) F1 alpha, thromboxane (TX) B2, PGF2 alpha and PGE2 concentrations in the incubation medium were measured by direct RIA. 6-Keto-PGF1 alpha production of adenomyosis was significantly higher than that of endometrium, myometrium and leiomyoma, especially in the menstrual phase. The production of eicosanoids in endometrial cyst was significantly higher than that of non-endometrial cyst and normal ovary. These results suggest that endometriosis is associated with increased eicosanoid production in vivo.