The behavior of the hemolymph amebocytes of Biomphalaria glabrata and Biomphalaria tenagophila was studied by means of the infection by the Schistosoma mansoni, using inoculation with Indian ink and fracture of the shell. A differential count of the amebocytes in the hemolymph was made with special attention given to the types of cell found in each sample. Histopathological evaluation of the molluscs exposed to the Schistosoma mansoni miracidia and analyses of the amebocytes were made. Correlation between the variance of the number of hemolymph amebocytes and tissue reaction was also made. The morphological study of amebocytes was carried out with the help of a phase microscope. An increase in granulocytes in Biomphalaria tenagophila occurred only when the molluscs were infected by Schistosoma mansoni, which suggests the specificity of the reaction to the parasitism. Comparing the results obtained with B. glabrata and B. tenagophila it is concluded that these molluscs show different amebocitary behavior in the presence of the diverse stimuli used.