Quantitative images of acoustic speed distribution in excised human tissues, in excised dog myocardium, and in in vivo female breasts were obtained by ultrasound computerized tomography. The in vitro study was carried over a temperature from 20° to 40 °C. Results indicate (1) acoustic speed in human tissues (except fat) increase monotonically with temperature in this range, (2) fat shows an anomalous decrease in acoustic speed around 35 °C, (3) average acoustic speed is higher in breasts with cancer and with fibrocystic disease compared to normal breasts, and (4) acoustic speed is a function of age. The reconstruction problem in ultrasound computerized tomography is unlike its x-ray analog because of the refraction and diffraction effects. Methods to correct for the consequent degradation are discussed. The backscattering properties of in vivo myocardial tissue of dogs were studied by a high-resolution B-scanner and the potential of (renovist and indocyanine green) as ultrasound contrast agents to quantitate perfusion in the myocardium will be discussed. [Work supported by NCI-CB-64041, HV 72928, HL-07111, HL-00060, HL-00170.]