Structural ceramic materials, in particular silicon nitride, have attracted interest for coal gasification technology at temperatures in excess of 1200 degrees C. In this study, a commercially available hot pressed silicon nitride is exposed for 200 h in a 0.4% H2S + 0.75% H2O + H-2 (balance) atmosphere, at 1200 and 1300 degrees C, simulating coal gasification environments. The crack growth behaviour of the as-received material is compared to that of the exposed condition. Measurements are carried out on specimens with small natural flaws (dynamic strength tests) and on specimens containing long cracks (chevron notch), both tested in four point bending. Results Of Strength tests (Modulus of rupture (MOR) and Weibull modulus) as well as toughness in both conditions are also presented. In view of the significant changes in the high temperature mechanical properties caused by crystallization of the intergranular glassy phase at triple points, further investigations of the effect of controlled devitrification seem surely worthwhile.