Eleven obese men with coexistent obstructive sleep apnea and chronic obstructive pulmonary disease underwent tracheostomy. Nocturnal polysomnography prior to tracheostomy revealed oxyhemoglobin desaturation associated with obstructive apnea. Following surgery, repeated polysomnography was performed to assess the effect of tracheostomy on nocturnal oxygen saturation. Non-apneic desaturation characteristic of that previously described in patients with "type B" chronic obstructive pulmonary disease was noted in six subjects. Oxyhemoglobin saturation in these six fell more than 8 percent below baseline waking and non-rapid-eye-movement (REM) sleep levels. These episodes usually lasted five minutes or longer, occurred almost uniformly during REM sleep, and were acutely ameliorated by low-flow (4 liters per minute) supplemental oxygen. The subjects with REM-associated desaturation did not differ from the subjects without desaturation by preoperative anthropomorphic, blood gas, or pulmonary function criteria. However, subjects with REM-associated desaturation tended to have lower right and left ventricular ejection fractions by pooled gated wall studies. It is concluded that patients with obstructive sleep apnea and chronic obstructive pulmonary disease should be re-evaluated after tracheostomy, since they may be at risk for continued oxyhemoglobin desaturation and progressive right ventricular deterioration despite adequate treatment of their apneic condition.