In this prospective study, 7 viral and 3 atypical bacteria antigens were investigated by immunofluorescence method during January 1999-May 2000 for the etiological diagnossis of respiratory tract infections. Respiratory tract secretions were obtained from children (group I, 76 cases) and adults (group II, 135 cases) who had symptoms of respiratory tract infections. Etiological diagnosis was reported as 45.4% in pediatric cases and 67.3% in adults. In group I and group II; the rates of Chlamydia pneumoniae was 17.8%, 13.3%; Mycoplasma pneumoniae 0%, 9.6%; influenza A virus 3.9%, 16.3%; adenovirus 3.9%, 14.8%; parainfluenza virus type 1 5.3%, 7.4%; respiratory syncytial virus 9.2%, 1.5%; parainfluenza virus type 2 3.9%, 3.0%; and influenza B virus 1.3%, 1.5% respectively. In 2.6% and 3.9% of the patients in two groups two or more etiological agents were identified. Parainfluenza virus type 3 and Legionella pneumophila antigens could not be determined in any of the patients. The advantage of immunofluorescence method for the etiological diagnosis and the effect of results to the rational antibiotic use were discussed.