<p>Previous research has demonstrated that gambling cues (e.g., flashing lights on poker-machines) can trigger an urge to gamble in poker-machine gamblers. However, the psychological mechanisms that promote the urge to gamble remain poorly understood. The present study explored whether reward responsiveness predicted urge to gamble and positive affect, and whether cue-reactive rationality, volitional control and imagery mediated these relationships. Ninety-three (45% male and 55% female) Australian regular poker-machine gamblers aged between 18 and 77 participated in an online cue-reactivity experiment. Participants initially completed the Problem Gambling Severity Index and Reward Responsiveness scale. Subsequently, at three time points (i.e., baseline, directly after a neutral cue and directly after a gambling cue) participants completed the rationality, volitional control and imagery subscales of the Phenomenology of Consciousness Inventory and two visual analogue scales that measured urge to gamble and positive affect. Analyses indicated that gambling cues triggered statistically significant increases in both urge to gamble and positive affect and these variables were statistically significantly positively correlated with reward responsiveness. Furthermore, only cue-reactive imagery mediated the relationships between reward responsiveness and the two outcome variables (i.e., cue-reactive urge to gamble and positive affect). These findings highlight the potential importance of targeting reward responsiveness and cue-reactive mental imagery in the context of exposure therapies for poker-machine problem gamblers.</p>