The thermal decomposition of 5-100 ppm H2S diluted in Ar was studied behind reflected shock waves at temperatures 1887 K less than or equal to T less than or equal to 2891 K and pressures around 1.3 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved concentration measurements of H and S atoms. Both the S and H concentration profiles showed almost linear increases at early reaction times with the S atoms exceeding the H atoms by a factor of 10-20. Therefore reaction R1, H2S + Ar --> H-2 + S + Ar (rate coefficient k(1)), was regarded as the initial step in the H2S decomposition. The rate coefficient k(1) was determined from the slope of the early S concentration profiles to be k(1) = 1.9 x 10(14) exp(-32860 K/T) cm(3) mol(-1) s(-1). The subsequent reaction between H2S and S atoms (reaction R2), H2S + S --> products (rate coefficient k(2)), was investigated in two different manners : first by evaluating the quasi-stationary S concentrations observed at longer reaction times in pyrolysis experiments of 100 ppm H2S and second by monitoring the decay of photolytically generated S atoms in laser flash photolysis-shock wave experiments with 30 ppm CS2 and 50-150 ppm H2S. Both groups of experiments covered the temperature range 1340 K less than or equal to T less than or equal to 2120 K and result in a rate coefficient k(2) = 5.7 x 10(14) exp(-7600 K/T) cm(3) mol(-1) s(-1). H concentration profiles measured during H2S/Ar pyrolysis were analyzed using a simplified reaction mechanism, which was able to-predict the experimental findings. In that case it was necessary to introduce a reaction channel (R2a), forming the reaction products HS2 and H, with an efficiency of 35-57% of the overall reaction R2.