Abstract. Viral and bacterial infections in 20 children under 3 years of age were studied in a day centre for 12 weeks. Febrile illnesses were found on one occasion in each of 11 children but no serious infection occurred. Pneumococci types 6, 9, or 19 were isolated from all children but more often from those with rhinitis or cough. The individual child had an average of 2 viral infections. Adenovirus types 1, 2, 5, coxsackievirus type B5, herpes simplex virus or respiratory syncytial virus was isolated from 12% of the oropharynx swabs and 40% of the fecal specimens. When a virus was first isolated from the oropharynx, the children were asymptomatic or had only rhinitis in 73% of the cases which might indicate that the dismissing of symptomatic children is of limited value in controlling the spread of infections in a day care centre. Cytomegalovirus was recovered from 22% of the urine specimens. Carrier frequency of cytomegalovirus was 23% in 40 other children attending one of 13 different day care centres. Because asymptomatic cytomegalovirus infections apparently occur frequently among small children in Sweden, it seems reasonable not to take pronounced measures of isolating the children in the relatively few recognized cases of cytomegalovirus infections.