The preparation and release of the International Conference on Harmonisation guideline on safety evaluation of human metabolites and the technical progresses in bioanalysis have triggered an intense debate on the value of absorption, distribution, metabolism and excretion radiolabelled studies in animals. Some authors have radically challenged the traditional approach whereas others, while accepting the need of significant changes, argue that these studies remain an irreplaceable component of the preclinical registration dossier. This paper reviews some of the representative positions and describes the potential evolution.