To evaluate controlled evidence on the efficacy of distance medicine technologies in clinical practice and health care outcome. Systematic electronic database and manual searches (1966-1996) were conducted to identify clinical trial reports on distance medicine applications. Three eligibility criteria were applied: prospective, contemporaneously controlled clinical trial with random assignment of the intervention; electronic distance technology application in the intervention group and no similar intervention in the control group; and measurement of the intervention effect on process or outcome of care. Data were abstracted by independent reviewers using a standardized abstraction form and the quality of methodology was scored. Distance technology applications were described in 6 categories: computerized communication, telephone follow-up and counseling, telephone reminders, interactive telephone systems, after-hours telephone access, and telephone screening. Of 80 eligible clinical trials, 61 (76%) analyzed provider-initiated communication with patients and 50 (63%) reported positive outcome, improved performance, or significant benefits, including studies of computerized communication (7 of 7), telephone follow-up and counseling (20 of 37), telephone reminders (14 of 23), interactive telephone systems (5 of 6), telephone access (3 of 4), and telephone screening (1 of 3). Significantly improved outcomes were demonstrated in studies of preventive care, management of osteoarthritis, cardiac rehabilitation, and diabetes care. Distance medicine technology enables greater continuity of care by improving access and supporting the coordination of activities by a clinician. The benefits of distance technologies in facilitating communication between clinicians and patients indicate that application of telemedicine should not be limited to physician-to-physician communication.