The purpose of this study was to demonstrate the efficacy of an exercise (walking) adoption intervention delivered through computer networks using electronic mail. The study involved 65 participants (17 males, 48 females), recruited through electronic bulletin board postings and flyers, who were randomly assigned to one of two conditions. The full treatment involved information, prompting, self-monitoring, goal setting and specific electronically delivered weekly feedback on walking performance. The minimal treatment condition involved all procedures except the specific feedback. During the 10 week program, participants in the full treatment who used the computer based system each week, compared to participants in the minimal treatment, walked more days (x̄=2.15 vs x̄=3.01), more minutes (x̄=76.17 vs x̄=107.73), more fitness minutes (x̄=57.90 vs x̄=88.41), and met ACSM minimum guidelines (frequency and duration) during more weeks (x̄=4.14 vs x̄=6.30). Analyses also showed setting and attaining goals was related to increased walking frequency. Survival analyses showed the full treatment condition particularly reduced and delayed dropouts of participants who were designated as contemplators or preparers (stage of change) at the start of the study. In addition, low enjoyment of walking was related to lower walking frequency and drop-out. In this highly computer-literate sample, computer attitudes were not related to infrequent interaction with the computer-based system. The study demonstrated the potential for using computer networks as a health behavior delivery system and showed the importance of goal setting and specific feedback, but also suggested the need for further tailoring of program offerings based on stage of change and other person characteristics.