We studied 145 children aged 7 years, who had been at day-care centers for at least 3 months during the 2 first years of their lives. The group was compared with a matched population of 145 children cared for at home. Of the 290 children, 212 participated in all phases of the study, which included a questionnaire to parents, skin prick tests with seven allergens, and a clinical examination. Day-care-center children had twice as much otitis media in infancy as "home" children (P less than 0.001), and they also tended to have more other infections. On the other hand, day-care-center children did not have more eczema in infancy, more cumulated atopic disease by the age of seven, or more positive skin tests than home children. When the groups were combined, an increased prevalence of cumulated atopic disease and positive skin tests was found in children with infections in infancy. We conclude that under the conditions of this study infections in infancy did not facilitate the development of hypersensitivity to allergens and atopic disease. The linked tendencies to develop infections and atopy could depend on some third factor.