A substantive amount of lab experimental evidence suggests that the norm of reciprocity has important economic consequences. However, it is unclear whether the norm of reciprocity survives in a natural and competitive environment with experienced agents. For this purpose we analyze data from a natural field experiment conducted with sales representatives who were instructed to randomly distribute product samples as gifts to their business partners. We find that distributing gifts to store managers boosts sales revenue substantially, which is consistent with the notion of reciprocity. However, the results underline that the nature of the relationship between market participants crucially affects the prevalence of reciprocal behavior.