The clinical hallmarks of asthma are wheezing and reversibility. Any disease that impairs air flow through obstructed airways may cause wheezing. Patients with true asthma may give a history of allergy and past attacks of dyspnea and wheezing occurring when exposed to allergens, inhaled irritants, upper respiratory infection, cold and humid air, exercise, and emotional stress. When encountering a wheezing dyspneic patient who does not report such a history, it behooves the physician to entertain the possibility that the patient may have a disease other than asthma. Chronic bronchitis, pulmonary emphysema, cardiogenic pulmonary edema pulmonary emboli, aspiration of gastric contents, and upper airway obstruction are the common causes of nonasthmatic wheezing. In almost every instance a wide spectrum of easily obtainable data, particularly historical, are available to alert the physician that the patient's dyspnea and wheezing are not due to asthma. Laboratory data are also readily available to buttress the correct diagnosis.