The ability of thymus-derived (T) cell depleted mice to eliminate a dose of the normally avirulent 11RX strain of Salmonella enteritidis was compared to that of normal mice by following the fate of the challenge organisms in the liver and spleen of both types of mice. Although the mice did not require normal numbers of T cells to survive infection with Salmonella enteritidis 11RX, T cell depletion reduced the ability of mice effectively to eliminate the organism from their tissues. In addition, T cell depletion abolished the ability of live Salmonella enteritidis 11RX vaccine to protect mice against a subsequent challenge with the virulent C5 strain of Salmonella typhimurium.