[en] Testing of performance characteristics of radiotherapy treatment units is an important part of the overall quality assurance efforts to fulfill and maintain the required high accuracy of dose delivery to the patient. Guidance on performance testing as well as recommendations on the desirable performance have been published, but these do not provide recommendations which are fully consistent or easily applicable. There seems to be a need for a more practical ''code of practice'' for performance testing, which would give a clear conception of the test methods and tolerance values. In this paper the general scheme of performance testing and the outline for the proposed code of practice is discussed. Some published recommendations on performance testing are compared and a possible new code of practice exemplified for one selected characteristic: quality of cross beam dose distribution. (author). 7 refs, 3 figs, 3 tabs