Etiology of acute lower respiratory tract infection in children from Alabang, Metro Manila. The etiology of acute lower respiratory tract infection (ALRI) was identified in 235 (43.8%) of 537 hospitalized children less than 5 years of age. Clinical evidence of measles was found in 258 (48.0%) patients, of whom 59 had a second viral infection. A viral agent was identified in an additional 121 patients, so that a total of 379 (70.6%) had viral infections. After measles, respiratory syncytial virus was the most common respiratory virus. Bacteremia was noted in 72 children (13.4%), occurring as frequently in children with measles (14.8%) as in those without (12.1%); Haemophilus influenzae and Salmonella typhi were predominant in the former, and H. influenzae, Staphylococcus aureus, and Streptococcus pneumoniae were prominent in the latter. The presence of bacterial antigen in urine was not helpful in identifying bacterial infection. Extrapulmonary and intrapleural complications, concomitant measles, complicated ALRI, female gender, and malnutrition were associated with increased mortality among children with ALRI. The importance of measles immunization, vitamin A supplementation for alleviation of defects associated with malnutrition, and timely antimicrobial therapy is emphasized. 