Social preference research has received considerable attention in recent years. Researchers have demonstrated that the presence of people with other-regarding preferences can have important implications in many economic dimensions. However, it is important to be aware of the fact that the empirical basis of this literature relies to a large extent on experiments that do not provide anonymity between experimenter and subject. It has been argued that this lack of experimenter-subject anonymity may create selfish incentives to engage in seemingly other-regarding behavior. If this were the case these experiments would overestimate the importance of social preferences. Previous studies provide mixed results and methodological di*erences within and across studies make it dificult to isolate the impact of experimenter-subject anonymity on prosocial behavior. In this paper we use a novel procedure that allows us to examine the impact of the exact same ceteris-paribus variation in anonymity on behavior in three of the most commonly used games in the social preference literature. Our data reveals that introducing experimenter-subject anonymity has only minor, insigni*cant, effects on prosocial behavior.