A technique for the determination of absolute (total) strain and stress within rock in situ. In this method, a smooth hole is bored in the rock and a gage is inserted to measure diametral deformation. The hole is then overcored with a large coring bit so that the cylinder of rock containing the deformation measuring gage is free to expand. The 3126 change in the diameter of the hole when the rock cylinder is free to expand is a function of the original stress in the rock and its elastic modulus.