Despite the link between inactivity and premature mortality, most adults exercise less than the Centers for Disease Control and Prevention (2008) recommends; thus, interventions to increase exercise are needed. The present study employed an Internet-based intervention to increase walking in 12 sedentary adults over 50 years of age. In Experiment 1, participants received monetary consequences for meeting an increasing series of step goals on at least 3 days during consecutive 5-day blocks. Across participants, steps increased 182% from screening to the end of the intervention, and 87% of step goals were met. In Experiment 2, goals were set using the same schedule as in Experiment 1, but no monetary consequences were provided for meeting them. Across participants, steps increased 108%, and 52% of goals were met. Across both studies, 11 of 12 participants increased their steps according to experimenter-arranged criteria. These results support the efficacy of an Internet-based intervention to increase walking in sedentary adults.