In order to evaluate the ELISA for schistosomiasis under the conditions of clinical practice, 1576 hospital patients were tested using a crude soluble Schistosoma mansoni egg antigen. Test sensitivity in detection of S. mansoni was found to be 96.2% and in S. haematobium 92.3%. The predictive value of positive results was high, reaching 88% at antibody levels three or more times the screening level. The test was considered by clinicians to be valuable for diagnosis and patient management, though it did not distinguish active from recently treated infections. Of 37 apparently false positive schistosome ELISA results only seven could be attributed to other helminth infections. Another nine patients had hepatitis. It is suggested that the antigens and antibodies of the two diseases are mutually cross-reactive, since reports have suggested a high increase of HBsAg patients with schistosomiasis.