The doping of diamond is an interesting topic for the production of microelectronic devices. During the last years the possibility of S-doping was shown and also n-type semiconductivity was described. Analytical measurements in the gas phase and thermodynamic calculations of the stable compounds were also reported, but the results were not always consistent. Thermodynamic calculations were carried out for a wide parameter range e.g. up to high sulfur concentrations, low and high pressures, various temperatures. The stability of various compounds e.g. H 2 S, CS, CS 2 , S, C x H y was calculated. Thermodynamic calculations showed that H 2 S reacts with methane to form the compound CS during filament activation. At the substrate temperature for diamond deposition (<1000 o C) there should be the reverse reaction from CS to H 2 S. Diamond deposition experiments were carried out in a hot-filament apparatus and H 2 S was used as a sulfur compound (between 400 and 2200 ppm H 2 S/CH 4 ). The thermodynamic calculations and diamond deposition results were compared with literature data.