A technique has been adapted to measure the relative change in the acoustic velocity of materials at frequencies up to 500 MHz with a maximum sensitivity of one part in 107. This technique is applied to the measurement of the temperature coefficient of the longitudinal-acoustic velocity of fused quartz over the temperature range 28-47 °C. The longitudinal velocity is observed to increase linearly over this temperature range. The temperature coefficient of the fractional longitudinal velocity increase of fused quartz is determined to be (1.075±0.025)×10-4 °C-1. This number is in agreement with the results of previous investigators and is the most accurate measurement available at room temperature.