Four patients (ages 43 to 51) with primary alveolar hypoventilation (PAH) syndrome were studied to characterize the pharmacologic augmentation of ventilation with intravenous doxapram hydrochloride. Doxapram hydrochloride evoked a rapid ventilatory increase of 50 to 100 percent in all four subjects with a consequent decrease in arterial CO2 tension. Blood pressure and heart rate measurements showed small increases during the doxapram infusion. These responses, however, were only sustained during the infusion, decreasing to their predoxapram level when the drug was discontinued. The ventilatory response to the drug was more marked in the pressence of hypoxia than during high O2 breathing, suggesting that the carotid bodies are a site of action for this drug in man. Doxapram hydrochloride can be an effective respiratory stimulant in patients with PAH.