Recent studies have shown that synthase for nitric oxide or scavenger enzymes is distributed throughout the endometrium. We have reported that endothelial nitric oxide synthase, originally identified in vascular endothelial cells, is distributed in glandular epithelial cells in the endometrium, peaking in the midsecretory phase. In addition, it is known that superoxide dismutase is distributed throughout the endometrium, varying with the menstrual cycle. Yet it is not clear how these enzymes are committed in the reproductive processes. Endometriosis is often complicated by infertility and miscarriage. Of particular interest is that these enzymes are overexpressed in the disease throughout the menstrual cycle. These findings strongly suggest that excessive amounts of free radicals are produced in endometriosis. Copyrightz1999S.KargerAG,Basel