Given the decreased rate of morbidity and mortality associated with physical activity, understanding the factors that enhance the efficacy of physical activity interventions is a priority. The present study examined the moderating effect of baseline enjoyment of physical activity on the efficacy of a physical activity intervention. Participants were 238 healthy low-active adults enrolled in Project STRIDE, a randomized, controlled, clinical trial comparing individually tailored print and telephone interventions to a contact control. Results indicated a significant interaction between intervention assignment (telephone or print intervention vs. contact control) and baseline enjoyment on physical activity at 6 months, as measured by the 7-Day Physical Activity Recall (z = 2.44, p < .05). These results indicate that our motivationally tailored physical activity promotion program may be more effective among individuals reporting greater enjoyment of physical activity at baseline, and suggest that attention be...