In this conceptual replication and extension of Rosenhan's study of civil rights activists, the sustained altruism (i.e., help that extends over time) of volunteers at a telephone crisis-counseling agency was examined. Using a prospective format, it was predicted that volunteers with a socialization history of exposure to nurturant parents who modeled altruism (autonomous altruists) would exhibit a greater degree of sustained altruism than those with a history of less nurturant parents who modeled altruism to a lesser degree (normative altruists). The altruism of the normative volunteers, however, was expected to increase given certain situational conditions (here, participation in a highly cohesive training group prior to the actual volunteer activity). As predicted, the rate of sustained altruism of normative volunteers in highly cohesive groups was increased to a level comparable to that of autonomous volunteers, while the altruism of autonomous volunteers was not affected by the training group experience. The implications of these findings for research on altruism and its development, as well as some applications to volunteerism, are discussed.