The impact of an incentive/reward intervention on college students' intoxication from alcohol consumption at fraternity parties was explored using a group-randomized trial. Participants included 702 college students (447 men, 225 women) attending fraternity parties in Blacksburg, VA. Six fraternities were randomly assigned to a control or experimental group, and each of these fraternities hosted two parties. The three fraternities in the experimental group hosted a baseline party first and then hosted an intervention party at which those having a blood alcohol concentration (BAC) level below 0.05 were entered in a $100 cash lottery. The three fraternities in the control group hosted two control (non-intervention) parties. For the experimental fraternities, mean BAC levels were significantly lower at the intervention parties (M=0.079) than the baseline parties (M=0.098) and the percentage of party-goers with a BAC below 0.08 was significantly higher at intervention parties (40.1%) than at baseline parties (30.6%). This field study supports the efficacy of differential reinforcement in controlling student intoxication at party settings.