Acute lower respiratory tract infection due to virus among hospitalized children in Dhaka, Bangladesh. The nature of acute lower respiratory tract infection (ALRI) in hospitalized children and of the associated viral agents was assessed in a study of 601 children less than 5 years old over a 24-month period. Of these children, 80% were less than 24 months of age and the ratio of boys to girls was 1.7:1. Pneumonia (86.5% of cases) was the most frequently observed clinical manifestation. Shedding of virus was detected in 21.1% of the children; the highest rate occurred in infants 0-5 months old (27%) as compared with a rate of only 12.5% in children 25-60 months old. Virus was detected in 33.3%, 32.8%, 21.2%, and 20% of the cases of tracheobronchitis, bronchiolitis, pneumonia, and croup, respectively. Among the viruses detected, 78% were respiratory syncytial virus (RSV) (91% of infections with this virus occurred in children less than 2 years old) and 14.4% were influenza virus types A and B. Of the RSV infections, 61% occurred in infants less than 1 year old. The case-fatality rate was 6.8% overall and was 4.8% in virus-associated cases. No consistent pattern of seasonal occurrence of viral infections was discerned. RSV was detected throughout the year, with increased prevalence from January to April. 