This study investigates the effectiveness of guilt-arousing communication in promoting prosocial behavior. By analyzing the distinct effects of anticipatory versus reactive guilt appeals, we contribute to the discussion of guilt appeals as drivers of prosocial behavior, especially blood donation. Research on persuasive communication provides the theoretical basis of our study and we validate our hypotheses by means of two 2 × 2 factorial between-subjects designs. We find that anticipatory rather than reactive guilt appeals are more effective in generating prosocial action tendencies. Compared to noninformational reference group influences, messages endorsed by members of informational reference groups yielded more favorable attitudinal responses. Besides their significant main effect, two-sided messages reinforce the favorable impact of anticipatory guilt appeals. The study concludes with practical implications for nonprofit organizations and public blood donor services as well as avenues for future research.