Sixty seven selected critically ill patients admitted to the wards and ICUs of chest departments, of both Alexandria University and Alexandria Armed Forces Hospitals, over a period of 17 months were included in the study. The aim was to evaluate quantitative culture methods in diagnosing lower respiratory tract infection [LRTI] and to identify the bacterial,fungal and mycoplasma pneumoniae isolates and to determine their antibiograms. Out of the 67 studied patients, 237 organisms were isolated, belonging to 17 species. Staph. aureus represented 34.3% followed by P. aeruginosa 32.8%, while H. influenzae and Ent. cloacae were isolated from 17.9% and 14.9% of patients respectively. M. pneumoniae was identified in 10.4% and C. albicans was isolated in 9% of cases only.