Endometriotic implants, like other estrogen-dependent tumors, contain both estrogen receptors and aromatase cytochrome P450 (P450arom), suggesting that at a local level, endometriotic implants produce estrogens, which may be involved in tissue growth through interaction with the estrogen receptors. P450arom is also expressed in the eutopic endometria of patients with endometriosis, adenomyosis, and/or leiomyomas, whereas neither P450arom protein nor mRNA is expressed in the eutopic endometria of normal menstruating women with cervical carcinoma in situ yet showing no other gynecological disease (disease-free). Examination of P450arom expression in endometrial biopsy specimens enables the physician to discriminate between the presence and absence of endometriosis, and may be used as an initial screening at outpatient infertility clinics. Copyrightz1999S.KargerAG,Basel