A fully digitized servo-control system, coupled with the automatic data acquisition facility, has been developed for a hollow cylinder apparatus (HCA). The closed-loop servo-control is based on a computer through which four individual stresses acting on the hollow cylindrical specimen can be independently changed using pneumatic regulators driven by stepper motors. The range of tests that can be performed in the HCA is considerably expanded to include boundary displacement controlled tests, as well as genuine stress controlled tests under generalized stress conditions involving principal stress rotation. This paper describes the detailed features both of the hardware and software of the servo-system. The experimental capabilities of the servo-system, together with its limitations, are discussed using test results that deal with particular aspects of the stress and strain paths associated with in-situ and laboratory loading.