Using the Transtheoretical Model of behavior change as a theoretical framework, a Stage of Exercise Scale (SOES) was developed. The ability of the SOES to differentiate between subjects classified into each of the theoretically posited stages was then studied in a sample of 178 female adults. Results showed that the scale was able to significantly and meaningfully differentiate between subjects classified by stage in terms of exercise energy expenditure (p < 0.0001, omega 2 = 0.18), physical activity energy expenditure (p < 0.0001, omega 2 = 0.15), and VO2peak ml/kg/min (p < 0.0001, omega 2 = 0.19). Stage-specific interventions have been successful when applied to other health behaviors and would appear to have promise for increasing our understanding of the exercise initiation and maintenance process. As such, researchers and practitioners may wish to use the SOES to begin testing the efficacy of stage-specific physical activity interventions.