Ultrasound mammography was performed with unique, high resolution equipment which displays changes in acoustic properties of tissues through a calibrated gray scale. Color coded isodensitometry was used to assist in the differential diagnosis of human breast cancer. The rate of agreement between the ultrasound and pathological diagnoses was 86.7%. The false negative and false positive rates were 7.6% and 18.5%, respectively. Three problems must be solved before ultrasound mammography can be used as a screening device: Additional clinical data must be accumulated. The number of ultrasonograms needed for diagnosis must be reduced. Special equipment designed for ultrasound mammography must be developed.