Earlier work on engaging in physical exercise when experiencing negative affect demonstrated robust associations with eating disorder (ED) behaviors and attitudes; however, measurement of the behavior was primitive, relying on one yes/no question that cannot capture much variability. We report on the development of a self-report measure, the Reactive Exercise Scale (RES), that disentangles the tendency to engage in exercise in response to negative mood cues from the tendency to engage in exercise in response to eating and body image cues, which themselves may be associated with negative mood. The measure also assesses exercising in response to positive mood cues.