Peritoneal fluid collected at celioscopy in infertile subjects was assayed for steroids and several prostanoids (PGE2, PGF2, TXB2, LTB4) as part of a study into pathophysiology of the female reproductive tract. Prostaglandins, produced massively in the pelvis, might interfere with fertility through various mechanisms (alterations in the egg implantation, follicle genesis, luteinization as well as tubal disorders). Our study of 54 patients showed a marked increase only of TXB2 out of the prostanoids assayed in overall endometriosis. In pelvic flogosis peritoneal LTB4 (and TXB2) were considerably increased if related to controls. This would suggest their role in the ethiopathogenesis of unexplained infertility (in relation to these pathologic patterns).