Because some studies have linked polymorphic variants of the estrogen-metabolizing genes CYP17 and catechol O-methyl transferase (COMT) with risk for hormonally related cancers, we sought to determine whether selected polymorphisms of these genes differed between women with and without ovarian cancer. From a population-based study of ovarian cancer, we analyzed DNA from a total of 480 cases and controls. PCR amplification was performed using primers that amplify restriction sites for MspAI (A2 polymorphism-CYP17) and NlaIII (Val/Met polymorphism-COMT). Digestion of the PCR products was performed. Genotypes identified by gel electrophoresis were assigned as homozygous wild type (WW), heterozygous variant (Wv), and homozygous variant (vv). Frequencies were compared using chi(2) or Fisher's exact tests. Logistic regression was used to calculate crude and adjusted relative risks (RRs) for ovarian cancer associated with possession of any variant allele overall, and within demographic, weight, and smoking history categories, and by histological subtype of ovarian cancer. A portion (68.9%) of cases either carried or was homozygous for the A2 variant of CYP17 compared with 53.9% of controls, for a RR (and 95% confidence interval) of 1.86 (1.26, 2.75; P = 0.003), adjusted for age, parity, oral contraceptive use, site of study, and family history of breast or ovarian cancer. The increased risk was most apparent for women >50 and women with invasive serous cancers. A portion (71.9%) of cases either carried or was homozygous for the Val/Met variant of COMT, compared with 76.9% of controls (P = 0.27). Although the inverse association of ovarian cancer with possession of a Val/Met variant was not significant overall, it was for mucinous tumors of the ovary, with an adjusted RR of 0.28 (0.13, 0.61; P = 0.0012). Possession of the A2 variant of CYP17 appears to increase risk for ovarian cancer, whereas possession of the Val/Met variant of COMT decreases the risk for mucinous tumors. Confirmation in other populations and further exploration of potential pathogenetic mechanisms will be necessary.