NOVELTY - Hydrogen generating apparatus (28) comprises hydrogen generating cells mounted to form a lower portion of the apparatus. Auxiliary devices mounted above the hydrogen generating cells are grouped along one side of the device. An open area free of auxiliary devices is provided above the hydrogen generating cells. A housing (30) is provided about the hydrogen generating cells, the auxiliary devices and the open area. It extends over the auxiliary devices and extends over the open area so that the housing defines a first height over the open area and a second height over the auxiliary devices.    USE - The apparatus is used in hydrogen generating assembly. It is used on motor vehicles to supplement the fuel used to drive the vehicle, e.g. transport truck.    ADVANTAGE - The hydrogen generating apparatus is formed and configured to permit it to be integrated with or mounted behind the stairs on the vehicle. It is positioned behind or as under a vehicle's stairs so that the stairs remain open and operational for their normal purpose to access the cab or other components of the vehicle, but the space below the stairs, becomes useful for housing some of the hydrogen generating components of the hydrogen generating assembly. The housing is formed to protect internal components of the hydrogen generating apparatus, and to support the weight of a person standing on the housing as may occur during use of the stairs by the person.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a hydrogen generating assembly comprising a stairs (10) including a step (14a-c) and the above hydrogen generating apparatus positioned behind the stairs so that the step of the stairs is exposed for use in front of the hydrogen generating apparatus. The stairs permit access to the hydrogen generating apparatus.    DESCRIPTION OF DRAWING(S) - The figure is a perspective view of a hydrogen generating assembly.    Stairs (10)    Step (14a-c)    Hydrogen generating apparatus (28)    Housing (30)