Introduction The association of obesity with hypersomnolence, hypoventilation, and polycythemia has become widely known during the past 5 years by the name "pickwickian syndrome."1A number of recent reports have described, in addition, twitching movements, cyanosis, periodic respirations, and congestive heart failure. Laboratory studies commonly reveal arterial hypoxia and hypercapnia and rightward deviation of the electrocardiographic axis.2-5 There are many problems of pathophysiology yet to be solved in the pickwickian syndrome. In this case study we have directed our attention to the phenomenon of periodic somnolence. The patient seemed particularly favorable for this investigation, since She showed strikingly regular cycles of sleep and arousal. Continuous simultaneous recordings of the electroencephalogram and of several parameters of blood gas levels and of respiratory function were made. An analysis of these tracings suggests certain relationships between respiration, blood gases, sleep, and wakefulness in the obese-somnolent patient. Report of a Case