Regular exercise habits depend on a variety of factors, including the reinforcing consequences of exercising. Extensive behavioral research suggests that reinforcing consequences reliably influence behavior (Catania, 1984), and Wankel (1985) suggests that adherence to exercise is likely only if a participant enjoys the exercise. However, focusing only on the reinforcing efficacy of exercise provides an incomplete analysis of reinforcing factors that influence exercise. Exercising involves choosing between exercise or nonexercise alternatives (Kendzierski & LaMastro, 1988), and the reinforcing effects of both exercise and competing nonexercise behaviors must be considered. One common example of a behavior that can compete with exercising is watching television. Watching television is a popular sedentary activity associated with low fitness (Tucker, 1986, 1990) and obesity (Gortmaker, Dietz, & Cheung, 1990). Based on the generally low rates of regular exercise (Caspersen, Christenson, & Pollard, 1986) and the high rates of watching television (Dietz & Gortmaker, 1985), it is reasonable to assume when given a choice, most people choose to be sedentary rather than to exercise. Observational research on adults (Brownell, Stunkard, & Albaum, 1980) and laboratory choice research with children (Epstein, Smith, Vara, & Rodefer, 1991) have shown adults and children choose inactive rather than active alternatives when both options are equally accessible. This choice maybe determined in part by the relatively strong reinforcement value of competing nonexercise behaviors and the relatively weak reinforcement efficacy associated with exercising (Epstein et al., 1991). © 1993 Taylor & Francis Group, LLC.