In this work, the Scanning Laser Acoustic Microscope (SLAM) is used to measure the spatial variation of the speed of sound in tissue, thereby providing a quantitative ultrasonic parameter for tissue characterization. The SLAM provides three different television type images. A laser scans the lower surface of the coverslip in order to detect mechanical disturbances induced by the 100 MHz ultrasonic energy which has passed through the specimen from below. The optical (laser scan) transmission image allows the operator to position the sample in the center of the 2 mm multiplied by 3 mm field of view. The acoustic image shows the amount of ultrasound energy passing through the sample. This signal is proportional to the envelope of the laser detector output. In this image, dark areas correspond to high areas of ultrasonic attenuation and light areas to low attenuation areas. The third image, the interference image, is produced by electronically mixing the laser detector output with a 100 MHz reference signal. 5 refs.