A resuscitation and inhalation device which can be used alternatively in each of two modes. The flow of oxygen or gas is controlled by a control valve, itself controlled by a movable member acted upon by the pressure of oxygen or gas in a chamber after having flowed passed the control valve. On meeting a preset maximum pressure, the valve member moves to close the control valve. The movable valve member is acted upon by a magnetic field which is adjustable, and the magnetic field strength sets the pressure at which the valve member moves. Oxygen or gas is admitted to the control valve by two alternative inlet valves, one for resuscitation with only oxygen or gas flowing through the mask, and one for inhalation, with a mixture of oxygen or gas and air or a second gas being fed through the mask.