A radioactive - pulse-flow - method has been developed for measuring H2S uptake by catalysts in a flow system during H2S/H-2 purging. As opposed to the classical pulse procedure, the S/(Ni + W) values calculated from radioactivity data obtained in a pulse-flow regime are in acceptable agreement with literature values by XPS and TPS methods. The temperature dependence of H2S uptake was identical for the NiW catalyst on different supports, whereas it was different for the NiMo catalyst. The uptake maximum was observed at 100 degrees C for NiMo/Al2O3, and at 200 degrees C for NiW/Al2O3 and NiW/SiO2-Al2O3. Periods of constant H2S uptake were observed, followed by periods of increasing H2S uptake after 35-65 min of sulfidation. This indicates the existence of permanent interaction between the sulfided catalyst and gas phase H2S.