Social cognitive theory is often implemented when researchers develop treatments and campaigns for health behavior change. Immersive virtual environment technology (IVET) enables novel explorations of health behavior modeling. In Study 1, participants were randomly assigned to one of three treatments: vicarious reinforcement, in which a virtual representation of the physical self (VRS) gained or lost weight in accordance with participants' physical exercise; an unchanging VRS; or no virtual representation. The reinforcement group performed significantly more exercise in a voluntary phase than those in other conditions. Study 2 separated reward (weight loss) from punishment (weight gain) and also explored model identification by contrasting the effects of a VRS with a VRO (virtual representation of an other); participants exercised significantly more when they viewed the VRS, regardless of whether reward or punishment was shown. In Study 3, participants were exposed to either a VRS running on a treadmill, a VRO running, or a VRS loitering, and we examined effects 24 hours after the experiment. Follow-up surveys revealed that participants in the VRS-running condition demonstrated significantly higher levels of exercise than those in other conditions. We discuss implications for media use and health communication.Social cognitive theory (Bandura, 1977(Bandura, , 2001) describes the power of a model demonstrating a behavior to encourage modeling by an observer. Several factors, including the similarity of the model, the observer's perceived ability to perform the behavior, and the rewards and punishments associated with