The results of bacterilogical investigations of urine specimens which contain chemotherapeutics or other germ-inhibiting substances are to be used only with limitation. In order to avoid malinterpretations of microbiological findings by unknown natibacterial autoactivity of the investigation material the routine proof of germ-inhibiting substances in the urine by means of a simple agar diffusion test has proved. By preservation of boric acid which is to be recommended for a longer transport of urine specimens which are to be investigated bacteriologically the results of the inhibitor tests is not falsified.