The crack growth behaviour at 1400°C of polycrystalline Si3N4has been investigated by use of dynamic- and static-fatigue tests on Vickers- and Knoop-indented bending bars, and the crack growth law determined as an exponential curve ofvagainstK1with exponentn= 20·7. No threshold behaviour was found for initial stress intensity factors greater than 1·75 MPa m1/2. The material investigated was a model Si4N4sintered without external addition of densification aids. The crack growth law found for this material may constitute a reference equation for polycrystalline Si4N4with an oxide grain boundary since it was obtained on a high-purity system and under experimental conditions for which the hypothesis of linear elastic behaviour was strictly satisfied.