Abstract The interpretation of gram stain smear of low respiratory tract secretions was frequently inaccurate, and these smears might be unreliable in predicting the causative bacteria of low respiratory tract infection (LRTI). Here two cases of lower respiratory tract infection were diagnosed by the microscopic examination of gram stain smear, while routine cultures were negative in 48h. The suggestion is that the techniques of gram stain smear paired to routine culture is valuable and should be encouraged in clinical practice for the management of lower respiratory tract infections.