The hepatosplenic form of schistosomiasis mansoni sometimes induces bleeding in oesophageal varices that requires surgical treatment. Although splenectomy is often necessary these patients rarely present with septic events, a finding that may be related to changes in the immunological system. To investigate the immunological profiles of patients with schistosomiasis, we studied the B- and T-lymphocyte counts and the immunoglobulin A, G and M (IgA, IgG and IgM) levels in patients treated surgically and in those who were not operated on. Patients who underwent distal splenorenal shunt, preserving the spleen, showed significantly increased T-lymphocyte counts compared with healthy controls. The IgM and IgG levels were significantly increased compared with the healthy controls in patients submitted to partial and total splenectomy, respectively. The IgM level also tended to increase in patients who were not operated on compared with the controls. These results suggest that chronic schistosomiasis may influence the immune system.