The dilatational and rotational wave velocities have been measured as functions of pressure and temperature for three gabbros, two basalts and a dunite. The pressure range was 200–6,000 bars. The temperature range was 25° to 300°C. and 400°C. for one sample. The maximum pressure is equivalent to 23 km of depth and the highest temperature is believed to correspond to 25 km. The data indicate a tendency for the velocity to reach a maximum somewhere between 10 and 20 km and then decrease slightly.