The mechanisms of immunity to salmonellae conferred by immunization with live vaccines were studied by adoptive transfer using the mouse-virulent strain Salmonella typhimurium C5 and innately susceptible BALB/c (ltys) mice. This organism cannot establish a sublethal infection in naive BALB/c mice. Animals immunized 2 to 3 months earlier with the S. typhimurium SL3261 aroA live vaccine were used as donors of serum, spleen cells, and mesenteric lymph node cells for naive recipients which were challenged orally with the virulent C5 strain. Simultaneous transfer of both immune serum and immune cells was necessary for protection. Simultaneously depleting the donors of CD4+ and CD8+ T cells by administration of antisera in vivo prior to cell harvesting showed that T cells were necessary for protection. The results demonstrate that both antibody and T cells are required for recall of immunity to oral challenge with virulent salmonellae in innately susceptible mice and suggest that the ability to elicit opsonizing antibody in addition to cell-mediated immunity is important for optimal protection induced by salmonella vaccines.