Apparatus for heating and humidifying respiratory gases comprise a housing, a gas permeable member and generating material. The housing includes an inlet adapted for connection to a tracheal tube and an outlet adapted for connection to a tube for passing respiratory gases. The inlet and the outlet are positioned so that respiratory gases passing through the housing pass therebetween. The gas permeable member, for example, a conventional heat and moisture exchanger member, is positioned in the housing between the inlet and the outlet and is adapted to exchange heat and moisture with respiratory gases passing through the housing. The generating material, for example, a carbon dioxide absorbing component, is located in the housing between the inlet and the outlet and is adapted to generate water, and preferably heat, available to humidify, and preferably heat, respiratory gases passing through the housing.