This is the first study examining motivation to participate in an HIV therapeutic vaccine trial of Remune and ALVAC. Trial participants (N=49) completed psychological measures at baseline. While 69% reported some personal risk in participating, 100% felt hopeful for societal benefits. Trial participants also reported high levels of existential well-being (e.g., "I believe there is some real purpose for my life"). Results suggest that HIV therapeutic vaccine trial participants are highly motivated by altruism and that participating in research may contribute meaning to living with HIV. Fostering altruism and responsibly promoting the societal benefits of research may facilitate trial participation.