A conceptual framework that identifies psychological and behavioral features associated with antecedents, experiences, and consequences of volunteerism is presented, and an inventory that measures 5 specific motivations for AIDS volunteerism is developed and cross-validated. Then a field study of 116 AIDS volunteers is presented in which a helping disposition, volunteer motivations, and social support (as antecedents), and personal satisfaction and organizational integration (as experiences) are used to predict duration of service over 2 1 2 years. Structural equation analyses indicate that dispositional helping influences satisfaction and integration but not duration of service, whereas greater motivation and less social support predict longer active volunteer service. The model is generalized to the prediction of perceived attitude change. Implications for conceptualizations of motivation, theoretical issues in helping, and practical concerns of volunteer organizations are discussed.