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The effects of a new benzodiazepine derivative Ro5-4200, on respiration and circula-tion were studied in 34 elderly male patients undergoing low spinal anaesthesia. A moderate increase in heart rate and arterial diastolic pressure occurred in two-thirds of the patients. Respiratory frequency was usually unaffected but there was a signifi-cant increase in Pa^oa measured at 5 and 15 minutes following intravenous administra-tion, with a tendency to return to control values at 30 minutes. It is suggested that the drug should be used only with caution in patients with restricted pulmonary function. Local tolerance to the drug was good; only one patient reported pain during injection. Recovery was rapid and dependable. The respiratory effects of the intravenous admini-stration of diazepam, when used to produce and maintain sleep in elderly patients, subjected to surgical intervention under some form of spinal analgesia, have already been reported (Pearce, 1974). No significant change in Paco3 was observed