This quasi-experimental field study assessed whether an incentive/reward intervention can change the drinking behavior and the subsequent levels of intoxication among college students attending fraternity parties. A total of 356 blood alcohol concentration (BAC) assessments, using hand-held breathalyzers, were obtained at two baseline and at two intervention parties at the same fraternity house. At the intervention parties, the students were informed they could win a cash prize if their BAC was below .05, and they were given nomograms to aid in monitoring their levels of intoxication. Mean BAC and the percentage of partiers with intoxication levels above .05 were significantly lower at the two intervention parties. More than twice as many partygoers were legally intoxicated (i.e., BAC > .08) at the two baseline parties than at the two intervention parties, indicating a clinically significant impact of the incentive/reward intervention. Greek-life students, in particular, were significantly less intoxicated at intervention parties, compared to baseline parties (p < .001).