Rewards not only increase motivation to train, but have also been shown to influence motor skill learning via activation of dopaminergic brain structures. In goal oriented tasks, receiving information about goal achievement has a rewarding value, which is further increased if performance has monetary consequences. Computer games often strengthen this kind of information by presenting explosions and other salient stimuli when a goal is achieved (e.g. a target has been reached). The current study investigates the outcome of an arm rehabilitation program, based on such a computer game delivered in two versions. Stroke patients are asked to use their impaired arms to perform goal oriented movements. Movements are translated into movements of a virtual arm on a computer screen. Goals are "meteors", threatening to destroy a planet on which they fall, if not caught by the virtual arm. One version of the computer game delivers state of the art graphics including a number of visual effects and, if the planet was protected successfully, information about a monetary reward, whereas the other version of the program delivers schematic graphic objects only. Training time and intensity are kept constant and outcome measures, including standard clinical motor assessments, are compared between the groups.