Experiments were carried out to determine the effect of discontinuities on the propagation of ultrasonic waves in samples of chalk and sandstone obtained from tunnel sites at Chinnor, Oxfordshire and Warrington, Cheshire respectively. In particular the effect of normal stress across a closed discontinuity was investigated. Tests to determine the wave velocity, attenuation coefficients and the effect of uniaxial compressive stress in intact samples of the rocks are also described. A brief review of work in this field is included and comparisons are made with results obtained by other workers. The 'Pundit' ultrasonic velocity measuring equipment was used for the experimental work and performed well in the Laboratory and under difficult conditions on site.