A general description is given of the procedure developed at the National Bureau of Standards for calibrating audiometers. The sources of calibration standards are presented, and there is a discussion of the physics underlying the present technique. Limitations on the validity of the threshold data are pointed out. A method for determining the calibration of audiometer earphones is described. Data on earphone response can be used to gain some insight into the malfunctioning of an audiometer, and the way in which this can be done is indicated.