We assessed the ability of a computerized outpatient medical record (MR) system, the Summary Time-Oriented Record (STOR), to communicate information to clinicians in two randomized single-blind studies. In the first study, physicians were better able to predict their patients' future symptom changes and laboratory test results from outpatient visits to an arthritis clinic when STOR was added to the standard MR than when the standard MR was used alone. In a separate study, the removal of the standard MR did not result in important decrease in the physicians' ability to predict their patients' symptoms and laboratory test results if they had the option of using the full paper record when they thought they needed it. In 134 (26%) of 514 visits, the physicians exercised this option. We conclude that for outpatient visits, the computerized record system STOR operationally added information to that supplied by the full paper MR. This improved flow of information could improve the clinical decision process.