This article aims to understand the motivational factors that influence individuals to donate blood, in order to support the social marketing measures for recruiting new donors. Based on theoretical research, a structural model was developed to analyze influences and interactions of constructs in individuals' intentions to donate blood. A field survey used a structured questionnaire with a sample of 346 individuals. The analysis included descriptive analysis, evaluation of psychometric consistency, and structural equation modeling with partial least squares estimation. Fear showed a negative influence and the reference group a positive influence on individual predisposition to donate blood. This indicated that social marketing for blood donation can be more effective in encouraging new donors if it remains focused on these two factors.