Monoclonal antibodies (moABs) MA54 and MA61, directed toward the O-linked mucin-type glycoprotein, have been established and showed highly specific reactivity with human ovarian cancer. Fetal intestinal and colonic mucosal cells expressed this antigen and meconium staining was also frequently positive. To investigate the characteristic of an epitopic carbohydrate recognized by these moABs, the reactivity of each moAB with meconium extract was monitored by solid-phase enzyme-linked immunosorbent assay with mono-, di-, and oligosaccharides. MA54 and MA61 react with meconium extract and the reactivities of these moABs are neuraminidase sensitive. Ovine submaxillary mucin had a strong inhibitory activity toward the reaction between meconium extract and MA54 as well as MA61, suggesting that these moABs recognize NeuAc 2-6GalNAc epitope in meconium. The second aim of this study is to investigate the possible application of moABs to diagnose ovarian cancer and to compare these levels with those of the CA125 antigen. While serum CA54/61 antigen levels were elevated in 44.4% of ovarian cancer cases and serum CA125 antigen levels were elevated in 86.7% of the same population, the use of both assays indicated a sensitivity of detection of 97.8% (44 of 45 patients) in the population studied.