The present research attempts to integrate behavioral and social science theories (e.g., theory of reasoned action, social cognitive theory, transtheoretical model) in assessing the effect and sources of social support of persons in various stages of physical exercise. Using multinomial regression to analyze the data collected via interviews from a sample of over 1,500 working adults in Jamaica, strong statistical support was found for the role of social support in initiating and maintaining exercise. The importance of various providers depends on the individual's stage of behavioral change. Health workers, relatives, and friends are important during early stages; while friends and physical trainers are important during later stages. Other results, limitations, and suggestions for future research are discussed.