By use of a capacitance diaphragm manometer operated at low temperatures, it is possible to measure the vapor pressure of cryogenic liquids without the uncertainties introduced by thermomolecular pressure gradients (thermal transpiration). Since the zero of this manometer is more stable at low temperature than at room temperature, useful sensitivity is increased. Because of the increased sensitivity at low pressure as well as great convenience and simplicity, this technique appears to have wide application in precise vapor pressure thermometry and similar work.