We designed a user-friendly computer program that permits physicians to use clinical and demographic descriptors to search a hospital's clinical database for purposes of patient care, teaching, and research. For example, the user can identify all admissions in which diabetic ketoacidosis was diagnosed, the serum bicarbonate level was under 12 mmol/liter, and the length of stay exceeded 7 days. Once particular admissions have been identified, all data stored in the computerized record can be displayed. Authorized persons can also request the patient's complete medical record for further study. Over a 5-year period, 895 doctors, nurses, medical students, and hospital administrators used Clin-Query to search the clinical database of Boston's Beth Israel Hospital 3724 times. They displayed detailed information on 72,489 patients and requested the complete medical record 5477 times. Responses to a computer-based questionnaire indicated that 16% of the searches were performed for patient care, 38% for clinical research, 16% for teaching and education, 12% for hospital administration, and 18% for general exploration. We conclude that physicians and allied personnel will repeatedly examine and analyze aggregate clinical information when they are provided with the appropriate tools.