Empirical studies show that intrinsic motivations increase the volunteer labour supply. This paper studies how monetary rewards to volunteers affect their intrinsic motivations. Using a sample of Italian volunteers, allowing to distinguish the type of volunteer, the paper shows that monetary rewards (extrinsic motivations) influence positively the choice to donate voluntary hours, while a low intrinsic motivation seems to decrease hours per week. Moreover, monetary rewards increase the hours per week of individuals with low intrinsic motivation. Thus, a crowding in effect on low intrinsic motivation might emerge for continuative volunteers. *Thanks