Mice singly housed without bedding at 5° C clear carbon from the blood more slowly than animals similarly housed at 25° C. Increasing the time of exposure to cold to 2, 18 or 72 hours does not further alter the rate of clearance. Bacteria are also "cleared" uniformly at the two temperatures when a highly virulent strain (SR-11) of Salmonella typhimurium is injected intravenously, but not when one of low virulence (RIA) is used. The RIA strain disappears from blood more slowly in mice at 5° C than in those at 25° C. This was demonstrated both by dilution counts and by labeling the bacteria with p32 and following the decline in radioactivity of blood with time. Livers of mice were sampled at times postinfection for radioactivity and for viable bacterial counts. Housing temperature had no effect on radioactivity changes, but viable counts were higher and decreased more slowly in mice at 5° C than at 25° C. These findings are believed to account, in part, for the greater susceptibility to infection with RIA that was previously seen in mice exposed to cold compared to those at 25° C.