Twelve patients with clinical, polysomnographic and oxymetric features of Sleep Apnoea Syndrome (S.A.S.) were recorded, after a 2-week wash-out period, during 2 nights without treatment and 2 nights after receiving 50 mg naltrexone at bed-time. Clinical symptoms improved immediately in four patients, within one month in three patients and after 3 months of treatment in the remaining five ones. Sleep Apnoea index as well as the number, duration and intensity of hypoxic events were dramatically improved by this treatment that has now been prescribed to 25 patients, for more than 2 years in 14 of them.