An authorization checking system for motor vehicles, in which a control unit in the motor vehicle, having a portable user-transponder, in an inquiry-response dialog using data exchange, checks, and allows or blocks, the authorization for unlocking or locking the vehicle doors as well as for starting or driving. In order to be able to modify the identifiers of user-transponders and components of the motor vehicle in a security-relevant manner, a so-called master-transponder is provided in addition to one or a plurality of user-transponders. The master-transponder has a particular, vehicle-specific identifier, using which, in a special-inquiry-response dialog, the authorization to carry out and complete special functions within a preselected scope, going beyond the access and start/drive authorization, can be checked, and allowed or blocked. For carrying out the special functions, the master-transponder has acoustical and/or optical display devices and/or input devices.