Counterimmunoelectrophoresis (CIE) was used to detect antibodies to Schistosoma japonicum soluble egg antigen in 118 sera from people living in a schistosomiasis endemic area in the Philippines. The sera were also tested for antibodies by the circumoval precipitin test (COPT); 53% were found positive by CIE and 48% positive by COPT. No significant differences were found between the tests (P = 0.18 by McNemar's test). Crossreactions with sera from patients with intestinal capillariasis and monkeys with experimental angiostrongyliasis were not found and no false reactions were detected with sera from “normal” controls. The CIE test as used in the present studies was found to be comparable to the COPT in sensitivity and specificity as related to cross-reactivity with sera from nematode infections such as intestinal capillariasis and angiostrongyliasis. Results are usually available quickly with nearly 70% of any reactions occurring within 1 h. The test should be of value in seroepidemiologic surveys in schistosomiasis-endemic areas.