Does paying people for helping undermine an important source of intrinsic motivation to help—the internalized sense of moral obligation? Self-perception theory suggests that individuals paid to help will infer that they have engaged in this behavior for the reward and not for reasons intrinsic to helping. Previous research has failed to find an undermining of intrinsic motivation that could be traced to the perception that helping was overjustified. We hypothesized that people's desire to appear morally motivated may have prevented the detection of overjustification effects. We therefore used a bogus pipeline procedure to convince subjects that we could tap their true attitudes, so that they would refrain from socially desirable but inaccurate self-presentation. The design consisted of two measurement conditions (bogus pipeline and pencil and paper) crossed with three activity conditions in which subjects recorded a text either to help a blind student for pay or with no reward, or to provide material for a study of vocal intonations. As predicted, payment for help undermined the sense of moral obligation only in the bogus pipeline condition. Unpaid helpers in this condition showed enhanced intrinsic motivation.