An etiological and environmental studies on Acute Respiratory Infection (ARI) had been done, in collaboration with the Sub. Division of Pulmonology, Department of Pediatric, Ciptomangunkusumo Hospital from November 1989 to February 1990. A total of 28 severe ARI were studied, male and female ratio were 1.0 : 1.1 and the Case Fatality Rate from the first 21 series were 14.2%, one boy and two girls. Specimens were collected from throat svab, bronchus aspirates and blood for viral and bacterial identifications. There were no mixed infection found, 57.1% of ARI were not caused by virus and 37.1% among these were bacterial and the rest was still unknown which might be caused by antibiotic treatment prior to admission. The bacterial were identified as Staph, albus 10,7%, Strept. alpha 10,7%, Candida 7,1% Staph aureus 3,6%, and Pseudo diptheri 3,6%. Viral isolation and serological test revealed Measles 14,5%, Myxovirus 7,1%; and Influenza A 0.04%. This study shows that by using selected medium and sera typing would give the same bacterial result with isolation from bronchus aspirate. For field study this method should be tried in order to know the etiology of ARI in the community. Compared with Myxovirus and Influenza A, Measles was the highest viral isolate on ARI episodes. This might be due to seasonal variation also. Field study had identified that the increase of smoking habit and air pollution from the kitchen smoke will increase the frequency of ARI episode per year. Therefore, restrain from smoking and/or good ventilation will reduce ARI.