The Philips TPS is a dedicated computer system primarily for the calculation and display or radiotherapy dose distributions resulting from multiple field and rotational beam teletherapy techniques. Although a comprehensive range of planning facilities is offered by the system, including calculations in a number of parallel slices taken through the patient, the amount of basic data required to program the system is modest. This paper describes the beam checks which are necessary in order to obtain the input data, and then examines how well the computed radiation beams compare with independently measured isodose distributions. Other features of the system are discussed and an assessment of its operational reliability is given. The recently developed interstitial program is not examined here.