We have previously shown thatCorynebacterium parvum (C. parvum), a nonspecific immunomodulator, partially protects splenectomized and nonsplenectomized mice when challenged with aerosolized pneumococci. We report here the effects of both splenectomy andC. parvumon the phagocytic function of the lavageable pulmonary alveolar macrophage (PAM).Groups of young adult male Sprague Dawley rats underwent splenectomy or sham operation 3 weeks before injection ofC. parvum1.5 mg IP (or saline) per animal. One week postinjection PAM's were harvested. The in vitro phagocytic indices (PI) for PAM incubated with tritiated thymidine-labeledS. aureusorStreptococcus pneumoniae, type 14, opsonized with normal rat serum, were determined.Splenectomy had no effect on lung weights, PAM yield, or PAM phagocytic activity.C. parvumadministration significantly increased spleen weight in sham-operated animals, but had no effect on lung weights, PAM yield, or phagocytic activity of either control or splenectomized animals.Splenectomy in the adult rat did not induce a phagocytic defect in the PAM and thus the lavageable PAM cannot be considered a significant site of the postsplenectomy defect. SinceC. parvumprotects animals from respiratory challenge withStreptococcus pneumoniaebut does not alter the number or activity of lavageable alveolar macrophages, we hypothesize thatC. parvumprotection is more likely related to our previous finding of an increased clearance of blood-borne bacteria by the expanded and enhanced reticuloendothelial system.