The promise and challenge of eHealth interventions.

Objective: To discuss how health behavior researchers can use the Internet to study and intervene on health behavior.

Methods: Describe how the Internet is increasingly able to offer a viable medium for health behavior intervention and the challenges and opportunities inherent in conducting online interventions and research.

Results: The challenges of eHealth include coping with the additional demands of development, finding ways to reach "hard-to-reach" audiences, and maintaining privacy and security while monitoring participant use.

Conclusions: Health behavior researchers and interventionists need to learn to apply eHealth tools to extend their ability to study and influence health behavior.