The cause of confusion, delirium and coma in patients with chronic bronchitis and emphysema in respiratory failure is still unclear. There is disagreement in the literature as to its etiology. It has been ascribed to hypoxia, systemic acidosis or to severe cerebrospinal fluid (CSF) acidosis. Since the clinical manifestations resemble hepatic encephalopathy, glutamine in CSF was determined concomitantly with acid base balance and PO2 in arterial blood and CSF. The patient material was divided into a control group (10 cases), chronic bronchitis and emphysema in respiratory failure but alert (10 cases), chronic bronchitis and emphysema – drowsy or comatose (8 cases), hepatic encephalopathy (7 cases) and patients with coma due to a cerebrovascular event (4 cases). It could be demonstrated that the ‘bronchitic drowsy’ group did not differ from the ‘bronchitic alert’ group in terms of acid base balance and PO2 in arterial blood and CSF. However, the ‘bronchitic drowsy’ group had a significant elevated glutamine level in CSF as compared to normal or ‘bronchitic alert’ group. This level was significantly less than the mean of the ‘hepatic encephalopathy’ group. There were 14 patients with signs of congestive heart failure in the hypercapnic group, 6 of these with mild signs of congestive failure were amongst the ‘alert’. All the 8 patients in the ‘drowsy’ group were in an advanced state of right sided cardiac failure. It is concluded that respiratory failure encephalopathy does not correlate well with acid base disturbances of either blood or CSF and correlates well with the glutamine levels of CSF which are raised in patients with concomi