In order to determine whether reversible alterations in ventilatory control are found in obstructive sleep apnea syndromes, 5 male patients 31 to 57 yr of age presenting with the syndrome were polygraphically monitored before and several times during the 6 months after tracheostomy. They also had a hypercapnic ventilatory response study before surgery and again 3 months after surgery during the daytime. A dramatic decrease in overall apnea index was seen immediately after surgery, but the number of central apneas and the central apnea index did not reach low values until several months after tracheostomy. Ventilatory response to CO2 improved in all cases after surgery.