Excess body weight, especially obesity, is a problem of increasing social significance. Because physical activity can both decrease body weight and prevent weight gain, it is an especially suitable target for behavioral intervention. A package intervention consisting of self-monitoring, goal-setting, and feedback was used to increase the physical activity of healthy adults. A combined multiple baseline and reversal design was arranged to evaluate the effects of the intervention the number of steps taken each day by participants, as recorded by a pedometer. The intervention increased the number of steps taken across participants, but there were no changes in participant body weight during the intervention. The results suggest that a relatively simple and low-cost intervention can be used to increase the physical activity of at least some adults.