Abstract: Sera of schistosomiasis japonica patients and of S. japonicum-infected mice were tested in immunoblots for their reactivity with adult schistosome proteins. We demonstra-ted the existence in S. japonicum of proteins sharing the diagnostic antigenicity of S. mansoni proteins, with approximately the same molecular weight of 31/32 KD, their reactivity with monoclonal antibodies and association with the schistosome gut. The proteins are, however, different between the two species at least in respect to one epitope and the relative mobility of one component. We confirmed the specificity of S. japonicum proteins by testing with sera of patients with other parasitic diseases. The data add support to the possible application of 31/32 KD schistosome proteins for serodiagnosis of sehistosomiasis Japonka.