Rats shifted from 4% to 32% sucrose displayed successive negative contrast by initiating significantly fewer bouts of licking than control rats maintained on 4% sucrose. No significant increase in dopamine (DA) efflux in the nucleus accumbens (NAc) was observed during consumption of 4% sucrose by rats shifted from 32%. In contrast, consumption of 4% sucrose by control rats was accompanied by a significant increase in DA efflux in the NAc, which remained elevated 10 min postconsumption. These data are consistent with the hypothesis that DA efflux in the NAc reflects the current incentive valence of sucrose reward and its influence on initiation of individual bouts of sucrose consumption.