The possibility of identifying patients who are liable to suffer complications after surgery was investigated in 482 patients with respect to three tests: the electrocardiogram, the ballistocardiogram, and a test designed to measure restrictive and/or obstructive factors affecting ventilation. There were 212 patients between 60 and 90 years of age, and in this group the incidence of unfavorable test results as well as postoperative complications was higher than in the younger age groups. There was little correlation between electrocardiography and the subsequent course of the individual patient. Increase in postoperative complications is noticed in patients having abnormal ballistrocardiograms and ventilation defects. The respiratory test was of value in enabling the surgeon to avoid major operations on the very few patients classed as prohibitive risks and to establish optimum operative conditions on patients with respiratory handicaps. The results of preoperative evaluation of the surgical patient by clinical impression without these tests proved to be of little value in geriatic patients.