The clinical findings for 105 children hospitalized with adenoviral infection were studied prospectively. In 82 children, the diagnosis was based on the detection of adenovirus antigen in the nasopharyngeal specimens and in 17 children in the feces. In the remaining six patients, findings from nasopharyngeal specimens were negative but a significant increase in CF (complement fixation) titers was detected. The clinical picture of adenoviral infection was characterized by high-grade (mean 39.4 degrees C) and prolonged fever (mean duration 5.4 days). Tonsillitis, otitis, and gastroenteritis were the most common illnesses. In 17% of the patients, no identifiable focus of infection could be demonstrated; nine children with no identifiable focus of infection had febrile convulsions. The WBC count and ESR varied from normal values to values seen in bacterial infections; thus it was difficult to distinguish adenoviral disease from a bacterial disease. Forty-five children were referred to the hospital due to infection unresponsive to antimicrobial therapy. The rapid detection of adenovirus antigen in nasopharyngeal specimens or feces proved to have a great clinical value in the diagnosis of adenoviral infections.