Polymorphysms of the three genes encoding phase 1 (CYP1A1, mEPH1, and CYP2E2) and the three genes encoding phase 2 (NAT2, GSTM1, and GSTT1) xenobiotic detoxication enzymes were typed by use of PCR in 74 patients with extragenital endometriosis. Distribution of the CYP1A1, mEPHX1, CYP2E1, NAT2, and GSTM1 polymorphic alleles in the patient group corresponded to that in the control group. At the same time, functionally defective genotypes GSTM1 0/0, NAT2 S/S; GSTM1 0/0, GSTT1 0/0; and GSTT1 0/0, NAT2 S/S were three, four and eight times more frequent among the patients than in healthy individuals. This observation suggests the existence of a distinct association between the functionally defective alleles of the phase 2 xenobiotic detoxication and endometriosis. Possible mechanisms underlying this association are discussed. It is suggested that typing of the NAT2, GSTM1, and GSTT1 genes can be useful for the assessment of the predisposition to endometriosis.