A computerized system of diagnosis (MEDITEL) was evaluated for its ability to consider a correct diagnosis in cases in which the correct diagnosis was not considered in the original differential diagnosis by physicians involved in the patient's care. The computer provided the correct diagnosis in 83% of the 33 cases studied when the information was entered by a physician and in 65% of cases when the information was provided by a medical secretary. The computer has the capacity to expand the physician's diagnostic capabilities. The MEDITEL system, at present, requires a precise vocabulary and is not designed to deal with intercurrent problems in patients with chronic disease.