A method is for diagnosing the driving capability of a driver of a motor vehicle, in which changes in driver condition are ascertained from physiological measured values derived from the driver while driving in the vehicle and evaluated, and if the changes are serious, a warning is issued or remedial actions are initiated, wherein the physiological measured values ascertained while driving in the vehicle are combined by a corresponding expert system with health-relevant data for the driver ascertained in stationary fashion, and with data indicating driver stress that are estimated in particular from the instantaneous traffic situation and instantaneous operating state of the vehicle, and the changes in the driver's condition are weighted with the estimated driver stress and interpreted. An apparatus for performing the method is characterized in that the expert system is implemented in an onboard computer of the vehicle which is connected via a bus internal to the vehicle to a mobile driver condition sensor suite that supplies the physiological measured values, to a memory/transfer medium that delivers the biographical data and/or the health-relevant data ascertained in stationary fashion, and to an ACC system and driving direction system internal to the vehicle.