The development of a new physical dating method for late Pleistocene tephrochronometry is described here. Tests of laboratory procedures applied to glass from independently dated samples show that the thermoluminescence (TL), additive-dose dating method can yield accurate ages for both proximal and distal tephra from a few hundred years to at least 400 ka. The technique involves purification of 4- to 11-μm glass by heavy liquid centrifugation, pre-TL readout heating at 50¿--75 ¿C for 8 days, and careful regression analysis of TL growth curves. Several unknown-age tephra are dated directly by this method for the first time. These include five ash beds from Summer Lake, Oregon (67--200 ka), a Sheep Creek Valley ash from Alaska (81¿9 ka), and ash from Nevada (200¿50 ka) correlated to the Wadsworth Tephra, an unknown ash (210¿30 ka) from Rye Patch Dam in Nevada previously correlated to the 400 to 600-ka Dibekulewe tephra, and ash 9M from Washtucna in eastern Washington (250¿30 ka). ¿ American Geophysical Union 1991