A method of determination of drive functions of slewing of a mobile crane's upper structure is presented in the paper. The purpose of their determination is to reduce load oscillations at the end of the motion. Drive functions for selected angles and durations of slewing have been calculated using a simple model of the crane and dynamic optimisation. Drive functions for intermediate angles have been determined by means of interpolation. Res ul ts of numerical simulations executed for the model of the crane are presented, taking into consideration flexibilities and damping in the cranes subsystems. Results obtained for drive functions determined using optimisation and interpolation algorithms are compared. An attempt to determine sensitivity of load positioning to selected operating parameters is also presented. Introduction of the notion of a positioning quality coefficient is proposed.