Objective: Given that only 25% of Americans meet physical activity recommendations, there is a need to develop and disseminate effective, evidence-based interventions to promote physical activity. The authors tested 2 delivery channels, telephone and print, to determine whether one was more effective in promoting physical activity. Design: The authors randomly assigned 239 healthy, sedentary adults to (a) telephone-based individualized feedback, (b) print-based individualized feedback, or (c) contact control. Both intervention arms were guided by a motivationally tailored, theoretically driven computer expert system. Main outcome measures: Physical activity as measured by the 7-day Physical Activity Recall interview. Results: At 6 months, both telephone and print arms significantly increased in minutes of moderate intensity physical activity compared with control, with no differences between the intervention arms. At 12 months, print participants reported a significantly greater number of moderate intensity minutes than both telephone and control participants, who did not differ. Conclusion: Results suggest that both telephone and print enhance the adoption of physical activity among sedentary adults; however, print interventions may be particularly effective in maintaining physical activity in the longer term. ((c) 2007 APA, all rights reserved).