A single-subject multiple baseline design across subjects was used to discern the effect of a token economy on the exercise behavior and cardiorespiratory fitness of individuals with Down syndrome. The subjects were three females ranging in age from 24 to 26 years, with estimated IQs between 32 and 56. The exercise behavior consisted of pedaling a cycle ergometer for 15 min each weekday at 50-60% of peak VO2 for 6 to 8 weeks. Subjects voluntarily pedaled the cycle ergometer during the baseline phase, and after stabilization entered the intervention phase at 5-day intervals. During the intervention phase, tokens that could be exchanged for preferred items were dispensed for a predetermined number of revolutions. Based on the data and calculations using the split-middle technique, it was concluded that a token economy can be used to increase exercise behavior. Resting heart rates decreased 12.2%, and submaximal exercise heart rates, averaged over three work stages, decreased 18.8% over the course of the study. The small sample size, variable subject response, and a malfunctioning gas analyzer call for caution in inferring any possible cardiorespiratory fitness training effect.