The systematic dosimetric control after all endocurietherapy implantations considered to be in conformity with the Paris System is often made manually from tracings of the radioactive threads and a series of tables which gives the strength of the dose as a function of the distance from the thread. The authors describe a calculating programme, developed in a small Hewlett Packard calculator associated with a printing-out apparatus (without graph tracings), which can determine the strength of the base dose and the tracing of the isodoses in the central plane for all radioactive implantations belonging to the field of application of the Paris System. A schematic representation of the organization of the programme includes feeding of information in the form of Cartesian co-ordinates; the geometric determination of the points for calculating the base doses, the calculation of the strength of the base dose, the reference dose, and doses at particular points in the central plane, and finally, tracing the isodoses. Several examples are presented, after which the authors discuss the advantages as well as the limits of this method.