A theory of altruism is presented which can be used to assess the effects of monetary reward incentives upon degree of altruistic giving. In this paper, the motive for altruism is hypothesized to be desire for self-esteem and the esteem of other people. However, one receives esteem only if the intent of the act is to help another person and not to benefit the altruist. The validity of altruistic motives is governed by the context in which help is given. If helpful acts are materially rewarded (i.e., payment for giving blood), then the helper's motives may not be purely altruistic. This has important ramifications for policy makers who may want to increase altruistic and socially responsible behavior by introducing economic incentives. These incentives may actually reduce people's altruism because material rewards may reduce the psychological and social rewards for helping. (Author/AV)