IgG and IgE containing circulating immune complexes (CIC), total serum IgE and parasite related IgE were determined in monoinfected patients with Schistosoma mansoni or S.haematobium and in patients with a mixed infection. IgE- and IgG-CIC and total serum IgE were significantly higher in the mixed infection group. There is considerable cross-reactivity between the crude S.haematobium and S.mansoni antigen preparations. The level of IgE-CIC is correlated to the levels of total serum IgE and parasite related IgE respectively. Furthermore IgE-CIC levels were related to the intensity of infection. Twelve out of 21 patients suffering from a monoinfection were reinvestigated 1-4 months after specific chemotherapy. Parasitological cure is followed by a significant decrease of total serum IgE and IgE-CIC, whereas parasite related IgE did not change significantly. The importance of the disappearance of IgE-CIC is discussed.