One of the key tools that organizations use to elicit prosocial behaviour is direct solicitations for donations. These have been shown to be the most powerful factor determining an individual’s prosocial behaviour in the forms of blood donations, charitable giving, and volunteering (Bekkers & Wiepking, 2011; Merz, Zijlstra, et al., 2017; Yörük, 2008). Nevertheless, not every solicitation results in a donation. This raises the question of what determines their effectiveness. In this study, we analyse the case of solicitations for voluntary and non-remunerated blood donations in the Netherlands. We apply the social-ecological systems framework (McGinnis & Ostrom, 2014) to explain variations in the effectiveness of solicitations. This framework highlights the embeddedness of individuals and their behaviour within a social and physical environment. Accordingly, our analysis considers how individuals compliance is related to factors on the individual level and the level of collection sites where blood ...