The paper discusses briefly the various known methods of measuring a.c. peak voltages in connection with h.v. testing, and mentions the errors and drawbacks associated with them.Results of a method of measurement, based on the principle of the diode peak voltmeter, are given whereby wave-shape and frequency errors are eliminated within wide limits. Comparisons are made with sphere-gap calibrations,1and also with a voltmeter of the “rectified condenser-current” type.2The method described, although primarily intended to apply directly to the h.v. connection, can be used in conjunction with a voltage transformer (or tertiary winding on the h.v. transformer).