Substoichiometric radioisotope dilution analysis has been applied to the determination of sulfur in coal. The experimental procedure involved the combustion of coal samples labelled with35S as sodium sulfate in a flowing oxýgen stream, collection of the combustion gases in hydrogen peroxide and substoíchiometric precipitation of barium sulfate. Samples of 0.2–10.0% sulfur were accurately determined with ±2% RSD by measuring the activity of the precipitates thus obtained and with comparison to standard samples carried through the same procedure. Analysis times of 15 minutes per sample were typical.