Immunological memory generated by infection with S. ratti was studied separately in the migratory and intestinal phases in mice. Protection against reinfection in the migratory phase was 96–98% at 2 weeks but significantly decreased to 60% at 12 weeks after the primary infection. However, protection in the intestinal phase was 96% even 12 weeks after the primary infection. Recall of immunity against the intestinal phase persists for longer than that against the migratory phase in mice.