Understanding the factors that influence alumni giving is a critical task of institutional marketers and development officers. To better understand the factors that influence alumni support, this research reports the results of a field experiment in which the effect that acknowledgement of alumni contributions has on their subsequent donation behavior is examined. Findings indicate that more elaborate acknowledgement programs that include personalized messages are most effective in increasing alumni donations. The age of alumni and their history of giving were also found to be related to giving behavior. (Contains 4 tables.)