Men who snore heavily have an increased incidence of hypertension, angina, stroke, and neuropsychologic dysfunction, which may be due to nocturnal oxygen desaturation. Nocturnal oxygen therapy might be beneficial to such individuals by improving oxygenation and relieving tissue hypoxia. Twenty-eight asymptomatic heavy snoring men were recruited for polysomnographic monitoring during sleep. During the first half-night, air was breathed through a nasal cannula, and during the latter half-night, 2 L/min oxygen was administered. Breathing air, 20 subjects demonstrated sleep apneas, hypopneas and nocturnal oxygen desaturation. Eighteen subjects had more than ten apneas plus hypopneas per hour. Thirteen subjects reached low oxygen saturation below 80 percent and eight below 70 percent. Only 13 of the 20 subjects showed improvement with oxygen therapy. Apneas alone were not decreased in frequency and were lengthened with oxygen therapy. Episodes of oxygen desaturation were improved by oxygen therapy and consequently, rates of hypopnea were decreased. Severe sleep apnea, hypopnea and oxygen desaturation are common in asymptomatic male snorers, and oxygen therapy is not always beneficial.