The goal of this research was to further our understanding of how the striatum responds to the delivery of affective feedback. Previously, we had found that the striatum showed a pattern of sustained activation after presentation of a monetary reward, in contrast to a decrease in the hemodynamic response after a punishment. In this study, we tested whether the activity of the striatum could be modulated by parametric variations in the amount of financial reward or punishment. We used an event-related fMRI design in which participants received large or small monetary rewards or punishments after performance in a gambling task. A parametric ordering of conditions was observed in the dorsal striatum according to both magnitude and valence. In addition, an early response to the presentation of feedback was observed and replicated in a second experiment with increased temporal resolution. This study further implicates the dorsal striatum as an integral component of a reward circuitry responsible for the control of motivated behavior, serving to code for such feedback properties as valence and magnitude.