NOVELTY - A method for heating and humidifying a reactant gas supply stream for a solid polymer fuel cell uses a combined heat and humidity exchanger. The reactant gas supply stream is directed to a reactant gas inlet port of the fuel cell. The fuel cell has a reactant gas exhaust system directed from a reactant gas exhaust port of the fuel cell.    USE - The method and apparatus are particularly suitable for use with air-cooled fuel cell systems and systems which employ near ambient pressure air as the oxidant gas supply.    ADVANTAGE - A simpler and more energy efficient means of pre-heating and humidifying reactant supply streams in a solid polymer fuel cell due to the heat and water vapor generated by the exothermic reaction in the fuel cell being used to directly heat and humidify a reactant supply stream.    DETAILED DESCRIPTION - A method for heating and humidifying a reactant gas supply stream for a solid polymer fuel cell is new in which the reactant gas supply stream is directed to a reactant gas inlet port of the fuel cell. The fuel cell has a reactant gas exhaust system directed from a reactant gas exhaust port of the fuel cell. The method comprises    (1) providing a combined heat and humidity exchanger comprising a supply stream chamber, an exhaust stream chamber and a water permeable membrane separating the two chambers;    (2) directing the reactant gas supply stream through the supply stream chamber upstream of the fuel cell reactant gas inlet port; and    (3) directing the reactant gas exhaust stream from the reactant gas exhaust port through the exhaust stream chamber.    Water and heat are transferred from the reactant gas exhaust stream to the reactant gas supply stream across the water permeable membrane.    An INDEPENDENT CLAIM is also included for a solid polymer fuel cell system including a solid polymer fuel cell and apparatus for heating and humidifying a reactant gas supply stream.    DESCRIPTION OF DRAWING(S) - The diagram illustrates the solid polymer fuel cell system:    solid polymer fuel cell stack (100)    reactant gas stream inlet port (110)    reactant gas stream outlet port (120)    flow path of a reactant stream (130)    flow path of an exhaust reactant stream (140)    water permeable membrane (210)