Breasts of 724 patients were studied by physical examination, mammography, and computed tomographic mammography (CTM) using a scanner designed for evaluation of the breast. Among cases in which CTM was not accompanied by use of contrast material, there were 60 malignant lesions, of which 10% were missed by mammography, 32% by CTM, and 8% by both. Among cases where CTM was supplemented by a 50 ml injection of 75% contrast material, there were 63 malignant lesions, of which 14% were missed by mammography, 16% by CTM, and 3% by both. Among cases where CTM was supplemented by a 300 ml infusion of 30% contrast material, there were 41 malignant lesions, of which 7% were missed by mammography and 5% by CTM, but none by both. Clinically, 22% of the malignant lesions in the infusion series were occult. There were 44 benign lesions in patients studied with the infusion technique. With mammography 68% were suspicious for malignancy, and with CTM, 56%.