Experiments were carried out to investigate the effects of ambient temperatures on the induction of transmissible gastroenteritis in feeder pigs 2 to 3 months old. Pigs maintained at a high temperature (30 +/- 2 degrees C) and exposed to the virulent transmissible gastroenteritis virus did not show clinical signs of the disease during their maintenance at the high temperature. On the other hand, a sudden decrease in the ambient temperature, either before or after virus inoculation, induced severe disease in feeder pigs exposed to the virus. However, continuous maintenance of pigs at the low temperature (4 +/- 1 degrees C) tended to somewhat reduce the frequency of occurrence of signs in proportion to the length of the maintenance periods at that temperature. Pigs raised at temperatures that fluctuated between 20 +/- 2 and 4 +/- 1 degrees C every 24 h developed profuse diarrhea. The duration of clinical signs was longer in pigs maintained under the fluctuating temperatures than in those at the constantly low temperature. With one exception, antibody against transmissible gastroenteritis virus was demonstrated in sera collected from pigs both with and without clinical signs. Antibody titers obtained, however, were somewhat higher in sera collected from pigs that had developed clinical signs than in those from pigs that had endured the infection without showing signs.