Ventilation (liters of air per minute) increases during an acute attack of asthma. Hypocapnia is the rule, although eucapnia may occur. This suggests both that respiratory center output is increased and that acidemia is not the major stimulus to augmented respiration. Mechanical receptors responding to change in end-expiratory respiratory system volume or airway dimensions, cortical stimulation to the medullary respiratory centers, and possibly hypoxemia function in concert to regulate ventilation in asthma. Newer laboratory techniques permit independent assessment of chemical and cortical components of ventilatory drive. These techniques have provided fresh insights into the effects of various therapeutic interventions upon respiration in asthma.