Male and female human volunteers were given diluted nasal secretions collected from patients with a common cold. One hundred and sixty-eight volunteers were chilled at 60 [degree]F and 80% relative humidity for 4 hours, 85 at 10[degree]F and 80% relative humidity, and 175 were placed in a comfortable chamber at 80 [degree]F and 30% relative humidity, either before or after the challenge with the infectious secretion. The incidence of colds was 32, 39 and 36%, respectively, in the 3 groups. These differences are not statistically significant. No relationship could be observed between frequency of experimental colds and season of the year, or differences between the temperature of the outdoors and experimental environment. Under the conditions of the experiments, chilling of the host did not make him more susceptible to the common cold. The significance of these findings has been discussed in relation to previous reports.