Empirical evidence is provided for the importance of non-reciprocal pro-social behavior of individuals in an anonymous, n-person pure public good setting. A unique panel data set of 136,000 observations is matched with an extensive survey.nEven under anonymous conditions, a large number of individuals are prepared to donate a not insignificant sum of money. Cooperation conditional on giving by specific other personsn(reciprocity) is present but the causal relationship is ambiguous. It is crucially important, whether, and in what way, one is asked to donate. Identification with the organization is also important.