Viral laboratory diagnosis was correlated with clinical and epidemiological data from 80 hospitalized children with acute lower respiratory infection (ALRI). They all were less than 5 years-old and were studied from May to September 1993. Fifteen percent of them were malnourished and 75% had some unsatisfied basic necessity. Nasopharingeal aspirates were obtained the first day of hospitalization, and diagnosis for respiratory viruses was performed by the immunofluorescence test with monoclonal antibodies. Routine laboratory determinations, x-ray studies, and clinical data were not conclusive to determine viral etiology. Forty-one percent of the children had a positive viral diagnosis: the most important agent was Respiratory Syncytial Virus (78.7%) followed by Adenovirus (9.1%), Influenza A (6.1%) and Parainfluenza (3%). The peak of incidence was observed in June and the majority of the patients remained hospitalized less than 10 days. Six children died: two of them had viral pneumonia and could not receive mechanical respiratory assistance. The percentage of children who received antibiotics was high, 61.2%, in spite of the fact that 34.7% of these patients had a laboratory confirmed viral etiology. The availability of rapid laboratory viral diagnosis may contribute to decrease the use of antibiotics and improve the management of patients.