Is there any lower limit to the radiological optimisation process?

The exemption from regulatory control of practices with very low level activity materials has an historical legal acceptance. The aim of this paper is to present some personal considerations linked with the application of the exemption criteria stated in the new ICRP recommendations. The report analyses and tries to clarify the apparent contradiction between the optimisation process and the practical threshold that a de minimis policy implies. Some practical cases that could appear now or in the near future are commented on. (author)