Sera from patients with schistosomiasis contain antibodies which react with keyhole limpet haemocyanin (KLH). This is due to carbohydrate epitopes shared by KLH and surface antigens of various Schistosoma species. Previous studies have used this cross-reactivity in enzyme-linked immunosorbent assay (ELISA) tests to distinguish between sera from acute and chronic cases in endemic areas. We describe a modification of the ELISA technique which distinguishes serologically between active schistosomiasis and normal sera. It has a sensitivity (88%) and specificity (94%) comparable with existing tests. If developed for routine clinical use, this test would be more useful in non-endemic areas than one which only detects acute cases.