The multitude of studies on the diagnosis of pneumonia published in the past year testifies to the fact that the best diagnostic strategy remains undefined. For community-acquired pneumonia, the etiologic agent can be diagnosed in a high percentage of patients if extensive serologic testing is used. Unfortunately, standard diagnostic tools, including blood cultures, have a low yield. Newer diagnostic techniques offer some hope for an etiologic diagnosis at a time when therapeutic decisions can be made. For nosocomial pneumonia in the nonventilated patient, transthoracic needle aspiration appears to have good accuracy with a low complication rate. For ventilator-associated pneumonia, research on diagnostic methods has yielded important insights into the disease process itself. Unfortunately, consensus regarding the most appropriate diagnostic tool has not been achieved.