Objectives: The objective of the present study was to determine the concentrations of CA 125, CA 15-3, CA 19-9, carcioembryogenic antigen (CEA), alpha-fetoprotein (AFP) and beta-2 microglobulin (B2MG) in patients with pelvic endometriosis. Method: Fifty women were divided into two groups: group A (control) had no endometriosis or other diseases, and group B consisted of 35 women with pelvic endometriosis. All women were submitted to serum determination of CA 125, CA 15-3, CA 19-9, CEA, AFP and B2MG. Samples were collected during the menstrual cycle and 1 week later. Results: Mean CA 125 concentrations were altered in patients with endometriosis, but all 50 patients studied presented normal CEA, AFP and B2MG concentrations. Small variations detected in CA 19-9 and CA 15-3 had no statistical significance. Conclusion: CA 125 is the only important marker in the diagnosis of stages III/IV of endometriosis, especially when blood samples for its determination are obtained during the first 3 days of the menstrual cycle. (C) 1999 The International Federation of Gynecology and Obstetrics.