Recent improvements in the ultrasonic computed tomography system at the University of Colorado Medical Center include use of separate transducer apertures for attenuation and velocity imaging. In addition, scanning time to acquire attenuation, speed of ultrasound and pulse echo data of each plane has been reduced to four minutes. Artifacts due to reflection of ultrasound from waves on the water surface and problems of aligning the scanning tank with the breast have been reduced by covering the water surface with an acetate membrane and polyethylene liner including a circular hole for the breast. A detailed description of the scanning system is presented in this paper, and examples are given which demonstrate many characteristics of the attenuation and speed of ultrasound in imaging of the breast. Five of the 42 patients scanned to date with the ultrasonic CT system also were among those imaged with a newly available pulse echo breast scanner. An example is given which illustrates the correlation between pulse echo and ultrasonic CT images.