Given that self-efficacy has emerged as a key construct in health psychology, this study set out to explore its utility in the context of blood donation as defined within the Theory of Planned Behaviour (TPB). An Ajzen and Fishbein-type questionnaire was administered to 100 undergraduate students at the University of Ulster, Coleraine. A hierarchical multiple regression analysis provided strong support for the role of self-efficacy as a major determinant of intention. It not only helped to explain some 73% of the variance, but also made a greater contribution to the prediction of intention than the other main independent variables of the model-past behaviour and self-identity. Demonstrating the utility of self-efficacy in the context of blood donor behaviour not only has several important practical implications, but serves to further highlight its importance within the TPB.