An account is given of the employment of an O2 concentrator (De VO2 955) in chronic bronchopneumopaths with respiratory insufficiency and pulmonary hypertension. An assessment was made of the gas supply modalities, particularly with Venturi masks. In patients with normal or low ventilation, 24% and 28% FiO2 masks gave suitable results, whereas those with a higher concentration were unusable, since the present FiO2 value was not reached. This was probably due to the fact that there is a fall in O2 concentration at high low flow rates, and as a result of an insufficient Venturi effect.