Direct radiometric measurements of the vapor concentration of H2S in equilibrium with aqueous diethanolamine absorbing solution were made using35S-labeled H2S. A thin-window Geiger-Müller tube viewed the gas phase only, while the absorbing solution was held in another part of the reaction flask. The equilibrium data were measured at H2S partial pressures below 0.01 mm Hg; the agreement with published results obtained by chemical analysis was good. The radiometric results were obtained very rapidly; a test run with seven data points took about two hours to complete. The results were applied to processes for reducing H2S concentrations in petroleum refinery fuel gases needed to meet tightening air pollution requirements.