Endometrial tissue from uterine disease-free women does not exhibitaromataseactivity. In contrast, aromataseenzyme activityand mRNA levels are readily detectable in endometriosis. PGE2stimulates both aromatase expression and activity in endometrioticstromal cellsvia promoter II region of the aromatase gene. This results in local production of estradiol, which induces PGE2formation and establishes a positive feedback cycle. This mechanism seems to contribute to continuous local production of estradiol and PGE2.