The results of numerical integrations of three‐dimensional equations of motion of ions subject to given electric and magnetic fields are presented. The fields represent those which may exist in the pinch phase of the plasma focus, although here they depend only on the radial coordinate. The ions initially have Maxwellian velocity distributions, and their trajectories are interpreted in terms of single‐particle constants of the motion. Two models of the axial electric fieldEzare considered. For strongEzaway from the axis, there is a cyclotron acceleration which leads to ion heating. For positiveEzon the axis, ions within a Larmor radius of the axis undergo very efficient acceleration; the results for this new model are in general agreement with experimental results.