1. Bacteriological and clinical observations on respiratory disease in a semiisolated infant population over a period of 2 years are recorded.
2. In two severe winter outbreaks of respiratory infection a parallel rise in the carrier rate of pathogenic organisms was noted.
3. The first autumn outbreak of colds seems to favor the dissemination of the pathogenic organisms.
4. The relationship of colds to the severer infections is roughly reciprocal.
5. Infants between 8 and 14 months of age are subject to the most severe infections.
6. The number of infants showing positive skin reactions to products of pathogenic organisms increases during the winter months.
7. The significance of these findings is discussed.