In a double-blind placebo controlled randomised study, the effects of almitrine bismesylate on the sleep induced Hb desaturations, associated or not with disorders of breathing, were tested. Patients (37-75 yrs, 8M and 2F) were affected by chronic bronchitis (out of any exacerbation) and obesity (weight excess at least 20%). They were known to have at least one nocturnal episode of hypoxemia (SaO2 fall higher or equal to 10%) with respect to the wakefulness level. Patients received either placebo or almitrine (1.5 mg/Kg/day) for 18 days and nocturnal polysomnography was performed both before and the last day of treatment. Almitrine induced an increase in PaO2 during wakefulness (p less than .05), an increase in mean SaO2 during sleep (p less than .01) and a decrease in the quantity of desaturation (Qd) during sleep, defined as the product of the mean desaturation by the duration of the episodes of desaturation (p less than .025). No clear effect could be observed either on the mean duration of the sleep disordered breathing (SDB) events or on their frequency whereas the desaturations due to them had a decrease.