A panel of 60 monoclonal antibodies (MAbs) reactive with repetitive epitopes of species-specific Schistosoma mansoni soluble egg antigen (SEA) was tested for performance in detecting circulating egg antigens. Two MAbs, 114-5B1-A and 114-4D12-A, which were highly reactive with two different repetitive carbohydrate epitopes of soluble egg antigen, were found to detect circulating egg antigen in the sera of S. mansoni-infected mice. The two MAbs also showed strong reactivity with two high Mr cercarial antigens present on the cercarial and schistosomular surface, while in the adult worms, antigens in the parenchyma were recognized. In two sandwich enzyme-linked immunosorbent assays (ELISA-5B1 and ELISA-4D12), each MAb was used as capture antibody and as conjugate, which resulted in assays with a lower detection level (0.2–0.4 ng) of the trichloroacetic acid-soluble fraction of soluble egg antigen (SEA-TCA)/ml. The antigen component(s) detected by ELISA-5B1 and ELISA-4D12 were 10,000 and 40,000 times more concentrated in the egg antigen than in the adult worm antigen, respectively. With both assays, in serum of heavily S. mansoni-infected mice, antigen became detectable from eight weeks postinfection (PI) onwards, with a striking increase at nine weeks PI.