Starting from bulk carbides, the removal by hydrogen of free carbon, oxygen from passivation and from carbidic carbon was studied in temperature-programmed experiments. Treatment of WC 1+ x O y with flowing hydrogen shows that the production of methane is maximum at about 700°C, above which it decreases. However, at the final pretreatment temperature, a residual partial pressure of methane is still observed, but this residual methane pressure decreases with temperature and disappears. After a few hours' treatment in hydrogen the final solid corresponds approximately to the stoichiometry WC without extra carbon. Such a treatment was monitored by X-ray diffraction in a diffractometer allowing temperature-programmed experiments from room temperature up to 900°C. It was shown that no metallic tungsten appears below 700°C. The amount of metal formed during treatment at 750°C is very small, and above 750°C it increases with temperature. However, even after a two hour treatment at 800°C, followed by treatment at 900°C, large proportions of carbide are maintained. No W 2C formation is detected. W 2C, after passivation, is very sensitive to hydrogen treatment, since a thermogravimetric experiment showed that, after a five hour treatment in hydrogen at 600°C, W 2C was completely decarburized into W. W 2C seems relatively stable at 400°C. A treatment of Mo 2C containing large amounts of free carbon in hydrogen at 700°C leads to MoC 0.47, that is, to clean Mo 2C. On the other hand, Cr 3C 2 behaves differently in hydrogen since some decarburization occurs before complete elimination of excess free carbon. By temperature-programmed X-ray diffraction in a O 2(2%)-N 2 mixture from room temperature to 500°C, it is shown that oxidation of WC to WO 3 starts at 400°C and is very fast at 500°C. No oxycarbides or intermediary oxides such as WO 2 were detected.