From September 1984 to May 1986, nasopharyngeal secretions were obtained from 519 children with some form of respiratory tract infection. The nasal secretions were screened for respiratory syncytial virus (RSV), rhinoviruses, adenoviruses, parainfluenza virus types 1, 2, 3, influenza virus types A and B, and enteroviruses by tissue culture virus isolation technique and/or enzyme-linked immunosorbent assay. A uniform questionnaire gave information about age, sex, individual signs and symptoms, findings of the physical examination and clinical diagnosis of the patients. RSV was detected in 119 (23%) specimens and was thus the most frequent causative agent of respiratory infections. After RSV, rhinoviruses were the most frequently recovered pathogens accounting for 60 (12%) cases of acute respiratory disease. A comparison of the individual signs and symptoms, the findings of the physical examination and the clinical diagnosis of RSV and rhinovirus infected children revealed that there was no characteristic clinical pattern associated with either of the two viral respiratory pathogens. According to our results, rhinovirus infections were a major cause of lower respiratory tract infections in hospitalized children less than or equal to 3 years old.