Lower respiratory tract infections are clinically important, because of their high incidence, as well as the significant morbidity they cause. Hence the great importance to diagnose the etiology of these infections and treat the patient with selective therapy. In this study 367 bacteria isolated from lower respiratory tract were identified (253 Gram negative and 114 Gram positive) and tested towards augmentin, ceftriaxone, lomefloxacin, ciprofloxacin, ofloxacin and erythromycin. The in vitro activity of such antibiotics against the clinical isolates was compared.