In our mechanical testing laboratory a crack growth monitoring device based on the ultrasonic time-of-flight diffraction technique has been developed It is intended to overcome some drawbacks or applicability limits of other methods In particular, the method should be applicable for bend specimens as small as Charpy type ones or even smaller (plane strain conditions required) as these are preferred dimensions in special fields of fracture mechanics testing (eg neutron embrittlement of reactor pressure vessel steels, testing of single crystals) (orig/HP)