In the last 2 years we have systematically treated 31 sleep apnea patients with 25-50 mg imipramine HCl given 30 min before bedtime. Imipramine treatment was attempted for nonoverweight patients with negative ear, nose and throat (ENT) findings and for patients who had not responded to weight reduction or ENT surgery (in all patients the apneas were not considered life threatening). Thirteen of the 31 (41.9%) patients, of whom 9 had central apnea, reported subjective improvement in diurnal and nocturnal symptoms within 10-15 days from the initiation of treatment. Sleep laboratory recordings conducted 1-5 months after the beginning of treatment revealed a significant decrease in the total number of apneas from 242 +/- 156 to 142.8 +/- 120.1 (p less than 0.01) in these patients. We concluded that treatment with imipramine may benefit selected sleep apnea patients particularly of the central type.