Abstract A discontinuous method has been developed for the simultaneous determination of H 2S and SO 2 in flue gases. The method is based on a pure gas phase separation whereby H 2S is adsorbed on a silica gel column impregnated with silver-sulphate (Ag 2SO 4) and potassium-hydrogensulphate (KHSO 4), while SO 2 is subsequently absorbed in a wash-bottle containing a slightly acidic hydrogen peroxide solution. Owing to the acid properties of the impregnated gel, SO 2 passes through the column. The experiments show that the penetration of SO 2 is quantitative while H 2S is adsorbed quantitatively on the column. The method permits the determination of amounts of H 2S in the range of 1–1500 mgNm −3 with a sampling time of 5 min and a gas flow of 0.2–4.0 1. min −1. The lower limit for the determination of SO 2 under the above conditions lies at about 1 mgNm −3. The separation of H 2S and SO 2 is not influenced by the presence of moderate amounts of water but the interference of ammonia is more serious. Ammonia is adsorbed on the column and the properties of the gel are changed so that SO 2 is also adsorbed. The method is still however, valid for H 2S. The interference from organic sulphur compounds is negligible with the procedure. Hitherto the method has successfully been used to analyse H 2S in ambient air in the ppb-range as 24-hr mean values.