T lymphocyte subpopulations in the peripheral blood of children with congenital cytomegalovirus infections and in controls were enumerated with monoclonal antibodies. Infants of less than 1 year of age with symptomatic infections showed significant increases in the proportion of suppressor cells and decreases in the ratio of helper to suppressor cells, whereas T lymphocyte populations in older symptomatic patients and asymptomatic infants and children did not differ from those in controls.