The activities of aspartate (AST) and alanine (ALT) aminotransferases and that of lactate dehydrogenase (LD) were measured in the homogenate of infected Biomphalaria alexandrina snails, the specific intermediate hosts for the parasite Schistosoma mansoni which is the cause of the disease schistosomiasis. The isoenzymatic pattern of LD was also studied in the infected snails tissue.