Book excerpt: Just prior to the 1982 Annual Meeting of the European Thyroid Association in Brussels, a number of outstanding experts in the field of X-ray fluorescence gathered at the Academisch Ziekenhuis of the Free University of Brussels in a joint effort to more clearly define the actual place and value of the latest newcomer among the techniques available for the in vivo assessment of thyroid function. It is the merit of Prof. M. Jonckheer to have organised this meeting and to have made available the work presented there to a larger public in the form of this monograph. Both, the meeting and the written accounts thereof are greatly appreciated by all thyroidologists who care for properly defining the genuine value of X-Ray fluorescence in scientific research and in clinical management of thyroid disorder. Three main conclusions can be drawn from the work presented 1. X-ray fluorescence has become a safe, convenient and reliable tool for measuring intrathyroidal iodine stores in vivo with an inter-assay reproducibility estimated at roughly 10% 2. X-ray fluorescence, used by expert hands, is a highly interesting tool to follow changes of intra thyroidal iodine stores in time, subsequent e. g. to the exposure of the thyroid gland to excess iodine 3. In contrast, no definite place of X-ray fluorescence as a technique in routine assessment of thyroid disease is yet at the horizon This latter conclusion may appear somewhat disappointing.