The assay of tritium-labelled substances in faeces requires conversion of tritium into either tritium gas (Payne and Done, 1958) or tritium-labelled water. Belcher (1961) and Kremenchuzky, Musso, Hoffbrand, and Viola (1967) used wet oxidation of faeces followed by liquid scintillation counting, while Burns and Glass (1963) used dry oxidation in a bomb calorimeter. There is a need for a reproduc...