Ultrasound imaging allows detection of pathologic change in muscle on the basis of increased strength of echoes. With current commercial equipment, however, there is no method of quantitation of the echoes representing muscle, and there is lack of uniformity in scanning methodology. We describe a specially constructed scanning system, designed to access the raw echo data directly from the ultrasound transducer, and allow display and measurement of the echo signals on a computer. In a study of 38 boys with Duchenne muscular dystrophy, aged 1 to 11 years, who had an ultrasound scan of the thigh muscle, 32 (84%) had abnormality on quantitation of the ultrasound echoes. The quantitative techniques we describe could easily be incorporated into the design of ultrasound scanners.