A gas dosing system for the quantitative deposition of low vapor pressure compounds onto surfaces in an ultrahigh vacuum system is reported. The dosing system is maintained at elevated temperature to achieve sufficiently high gas pressure for rapid transfer to the surface. Dosing is achieved through a heated calibrated leak valve which connects the high temperature source system to an internal tubular doser. The leak valve and the internal doser head are heated to a higher temperature than the source system to prevent condensation of the compound., The quantitative behavior of this doser is demonstrated for two low vapor pressure compounds. (C) 2003 American Vacuum Society.