NOVELTY - Cell stack (10) has a fuel cell (FC) stack and a humidification cell stack having cell(s) provided with a moisture exchange (ME) membrane. Each humidification cell has oxidant and fuel flow channels. The ME membrane separates the oxidant and fuel flow channels, so as to permit transfer of moisture from humidified oxidant discharged from the FC stack to dry, incoming fuel, flowing to the FC stack.    USE - Cell stack is used for electrochemical fuel cell of proton exchange membrane (PEM) type.    ADVANTAGE - Since the humidification cell stacks are provided at either end of the fuel cell stack, temperature of the entire fuel cell stack is stabilized, and hence all the individual fuel cells are operated substantially at the same temperature. Additionally, by providing humidification cells or cell stacks on both ends of power generation cell stack (20), water is recovered before it hits the power generation cells.    DETAILED DESCRIPTION - The fuel cell stack contains at least one fuel cell, a humidified oxidant inlet (24), an oxidant discharge (25), a humidified fuel inlet (26) and a fuel discharge (27). The humidification cell stack (30) comprises a discharged oxidant inlet (36) connected to the oxidant discharge, a humidified fuel outlet (34) connected to the humidified fuel inlet, a main fuel inlet (32) and a main oxidant outlet (38). The oxidant flow channels (21, 35, 43) are connected between the discharged oxidant inlet and the main oxidant outlet. The fuel flow channels (22, 33, 45) are connected between the main fuel inlet and the humidified fuel outlet.    An INDEPENDENT CLAIM is also included for method of humidifying at least one stream supplied to the fuel cell stack.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic view of fuel cell stack comprising humidification cell stacks.    Cell stack (10)    Main power generation cell stack (20)    Oxidant flow channels (21, 35, 43)    Fuel flow channels (22, 33, 45)    Humidified oxidant inlet (24)    Oxidant discharge (25)    Humidified fuel inlet (26)    Fuel discharge (27)    Humidification cell stack (30)    Main fuel inlet (32)    Humidified Fuel outlet (34)    Discharged oxidant inlet (36)    Main oxidant outlet (38)