Lower respiratory tract infection (LRTI) is one of the major health problems in developing countries such as Indonesia. According to the National Household Health Survey conducted by the Ministry of Health in 1992, LRTIs still rank fourth as the main cause of death in Indonesia. The problem of LRTIs could be simply managed as long as the causative organism can be identified and the proper antibiotic known. In some occasions, it is not quite so easy to identify the causative micro-organism, especially in lower tract infections. There are several methods of obtaining specimens from LRTIs for cultures. The easiest, most simple way is to collect expectorated sputum. Unfortunately, because of the high rate of contamination by upper respiratory tract flora, this method is not reliable. Recognizing the difficulties with routine expectorated sputum cultures, two alternative approaches have been suggested. One approach is to bypass potential expectorated sputum 'contaminants' in the oropharynx by transtracheal aspiration or transthoracic aspiration. The second approach is to modify the usual technique of processing expectorated sputum by either washing techniques or by quantitative cultures. Azithromycin and clarithromycin are chemically related to macrolide erithromycin. Both antibiotics retain the traditional macrolide spectrum of activity against gram-positive and atypical pneumonia pathogens, while demonstrating improved activity against gram-negative bacteria. The American Thoracic Society (ATS) recommended the use of macrolide for outpatients with community-acquired pneumonia, without comorbidity and 60 years of age or younger. A total of 34 outpatients with acute LRTIs were open-comparative, randomly allocated to treatment with the new macrolide in Persahabatan Hospital, Jakarta, 1996. The purposes of this study were: (i) to identify the causative micro-organisms; and (ii) to evaluate the clinical efficacy of the new macrolide in these infections. Azithromycin 500 mg was given orally once a day for 3 days and was administered 1 h before or 2 h after every meal. Clarithromycin 500 mg was given orally every 12 h for 10 days. The diagnosis of the patients were: 16 with pneumonia, 10 with acute bronchitis and 8 with acute exacerbation of chronic bronchitis. In this study of 34 patients, the sputum specimens were washed with N acetylcysteine before culture and we could only detect micro-organisms in one patient. Before treatment, we found 47 strains in 33 (97.05%) patients and after treatment we found five strains. From serological examination, only four (11.76%) atypical bacterial were detected. The most frequently found microorganisms were 23 strains of Klebsiella pneumoniae (40.42%), 10 of Streptococcus alpha haemolyticus (21.26%), five of Streptococcus pneumoniae (10.63%) and five of Staphylococcus aureus (10.63%). The atypical bacterial were: two Legionella pneumophila, one Mycoplasma pneumoniae and one Chlamydia pneumoniae. The clinical efficacy of new macrolides were 100% and the bacteriological responses with eradication of 94.12% vs 70.59% of isolates in the azithromycin and clarithromycin groups are shown in Table 1. There were no adverse reactions detected in the two treatment groups until the end of the study.