The influence of two contrasting environmental temperatures upon time survival rates of premature infants in the first 5 days of life was studied. Infants who were placed in incubators with an air tamperature of 31.7°C (89°F) had a higher survival rate than controls who were in incubators maintained at 28.9°C (84°F). In this clinical trial a sequential, matched-pairs plan was used to evaluate the differences in survival under the two study conditions.