Sixty infants in whom clinical symptoms suspected of cytomegalovirus (CMV) infection were studied. CMV infection was found in 50% of the subjects. The diagnosis was based on studies of specific antibodies and isolation of the virus from urine and/or throat swabs. In most of the children the examinations were repeated several times, and clinical observations continued for 1 to 42 months (avg. 18 months). IgM-class antibodies were detected in 26 children and in 18 the virus was isolated. In 3 infants, isolation of CMV virus was the only evidence of active infection. Persisting viruria (avg. 11 months) and long-term presence of Ig G antibodies, even to 44th month of life were also observed. Congenital infection was diagnosed in 4 infants; the remaining ones acquired the infection during the perinatal period or later. In 7 cases transfused blood cannot be excluded as the source of infection. The clinical symptoms manifested in infected and non-infected children were similar. There was a statistically significant increase in the occurrence of hepatomegaly, splenomegaly, hyperbiliru-binemia and diarrhoea in infected children. Congenital abnormalities were found in 10 infected children, including 4 cases of congenital cytomegaly.