Following splenectomy (SPLY) there is increased retention in the lung of injected particulate matter and an increased mortality from sepsis in experimental animals. Since it has been shown that autotransplanted splenic tissue (AST) decreased elevated pulmonary particulate retention after SPLY and improved the survival of animals following SPLY and sepsis, we attempted to determine whether the protective effect offered by AST was specific to the spleen. To determine this, four groups of rats were studied: Group I—sham; Group II—SPLY; Group III—received 100 mg of heterotopic AST in an omental pocket after SPLY; and Group IV—received 100 mg of heterotopic muscle tissue from the abdominal wall (AMT) in an omental pocket after SPLY. Six days after the above procedure, reticuloendothelial (RES) function was evaluated. The results indicate that both AST and AMT significantly decrease the abnormal pulmonary retention of particulate matter following SPLY. However, hepatic lipid retention was greater in the AMT than the AST group. Survival following sepsis was studied in other animals from Group I, II, III, and IV. At 7 days after the original operation, the cecum was ligated and punctured (CLP) and then removed 16 hours later. The splenic- as well as muscle-implanted animals showed significantly higher survival rates than the splenectomized animals. We therefore conclude that survival after SPLY can be improved by implanting either a fragment of the spleen or the muscle in the omental pocket. Since both tissues appeared necrotic at 7 days following implantation, the decreased pulmonary particulate retention and improved survival following SPLY and sepsis appear to be due to the presence of a necrotic tissue irrespective of its origin. These results suggest that the early effect of an implanted tissue is a nonspecific stimulation of phagocytosis. © 1983 by The Williams & Wilkins Co.