We study human manipulation tasks requiring the coordination of two arms with grasps that rely on frictional forces for stable prehension. Specifically, we investigate tasks in which an object is grasped with open palms and moved from one position and orientation to another in a horizontal plane. We are particularly interested in the force distribution and object trajectory in voluntary, relaxed movements. The first important observation is that there is a significant degree of repeatability in the kinematic data across trials and across subjects. Secondly, we show that all trajectories are characterized by asymmetries that cannot simply be explained by the dominance of one arm over the other. Finally, we show that the internal forces can play an important role in trajectory generation. While these are repeatable across trials, they vary significantly from subject to subject. The results of this paper are potentially important for the design of bimanual machine interfaces and for robot control and coordination.