In a study of ten patients with obstructive pulmonary disease, 0.11 mg/kg of diazepam produced small reductions in VE/VT, and &OV0312;o2in most of the subjects. Paco2rose in every subject (mean increase 3.5 torr) and most subjects had increases in VD/VT. In half of the subjects there were reductions in slopes of the ventilatory responses to CO2or in VE57. The presence and magnitude of these changes were unrelated to pre-existing mechanical or gas-exchange abnormalities.