Abstract: This paper deals with a method forming the error signal to control the direction of the longitudinal axis of a vehicle by way of the optimal rotation axis. In order to control rotation around the longitudinal axis, the ways to form the error signals in the case of roll stability and slope stability are considered. The analytical formulae are developed in detail. As examples of application of this method we have also discussed how to form the error signals sensored by a three gimbal platform or a group of stra-pdown rate gyros mounted in the vehicle. Corresponding block diagrams are presented.