This study reports data from a field experiment that was nconducted to investigate the relevance of gift-exchange for charitable ngiving. Roughly 10,000 solicitation letters were sent to potential donors nin the experiment. One third of the letters contained no gift, one third ncontained a small gift and one third contained a large gift. Whether a npotential donor received a letter with or without a gift was randomly ndetermined. We observe strong and systematic effects from including gifts. nCompared to the no gift condition, the relative frequency of donations nincreased by 17 percent if a small gift was included and by 75 percent for na large gift. Consequently, including gifts was highly profitable for the ncharitable organization. The contribution of this paper is twofold: first, nit shows that reciprocity is an important motive for charitable giving, in naddition to the warm-glow motive. Second, the paper confirms the economic nrelevance of reciprocity by using field data. This extends the current body nof research on reciprocity, which is almost exclusively confined to nlaboratory studies.