A technique for the determination of absolute (total) strain and stress within rock in situ. This method involves (1) installation of strain gages on the rock surface; (2) cutting of a slot in the rock between the strain gages so that the surface rock is free to expand; (3) installation of a "flat-jack" (hydraulic pressure cell) in the slot; and (4) application of hydraulic pressure to the flat jack until the rock is restored to its original state of strain. The original stress in the rock is presumed to be equal to the final pressure in the flat jack.