Women in the professional e-mail counseling group were more likely to lose weight if they perceived fewer barriers to and higher self-efficacy for healthy eating and activity. Greater weight loss in the peer-led discussion group was observed for women with lower self-efficacy and higher perceptions of barriers. Interpersonal support did not moderate the effects of the interventions.Their baseline perceptions of behavior-specific cognitions moderated their relationship with the type of intervention and weight loss success. These findings, although exploratory, may assist in matching women to Web interventions that would best maximize weight loss success. Further research is needed.