Salmonella typhimurium did not inhibit fusion of lysosomes with the phagocytic vacuoles in infected macrophages and caused no increase in cyclic adenosine 3':5'-monophosphate. Glutaraldehyde-killed bacteria showed rapid ultrastructural degeneration within the phagolysosomes. In contrast, untreated bacteria were resistant to digestion by lysosomal enzymes. Intracellular survival of this species appears to depend on resistance to, and not evasion of, lysosomal enzymes.