Serum sialyl-Tn, sialyl-Lewis Xi, CA 19-9, CA 125, carcinoembryonic antigen (CEA), and tissue polypeptide antigen were measured in 65 women with early-stage ovarian cancer (45 stage I and 20 stage II cases) and 317 with benign pelvic masses. As a single assay, sialyl-Tn showed the best sensitivity and specificity, 46 and 92%, respectively. CA 19-9 detected the greatest number of cancer patients but had the lowest specificity. The combination of sialyl-Tn, CA 125, tissue polypeptide antigen, and CEA seemed to perform the best, with a sensitivity and specificity of 71 and 76%, respectively. The combination of sialyl-Tn, CA 125, and tissue polypeptide antigen gave similar results and may be more cost-effective. However, one-fifth of the patients with early-stage cancer still showed up as false negatives even with use of the six markers in combination. Approaches other than serum assay alone will be needed to detect all malignant pelvic masses at an early stage.