We studied 15 patients submitted to splenectomy. Humoral immunity was studied with protein electrophoresis and quantification of immunoglobulins; cellular immunity was studied by total and subpopulation lymphocyte counts and evaluation of phagocytosis. Increased levels of IgG, IgM and IgA, a decrease in circulating T-lymphocytes and an increased phagocytosis was seen after operation. These findings correlated to the presence of viral and parasitic infections postoperatively. Preoperative antipneumococcal vaccination prevented infections by this agent. Thus, appropriate preventive measures must be taken to deal with altered immunological responses after splenectomy.