[Blood cell labeling: retrospective and prospects]

The labelling of blood cells in vitro for subsequent in vivo studies was one of the earliest applications of radioactive tracers in clinical medicine and laid the foundations for many important contributions to the advancement of knowledge of human blood cell pathophysiology. The characteristics required for satisfactory clinical studies, the mechanisms of cell labelling, the problems of radiation of chemical damage to the labelled cells and some examples of modern clinical applications are described and discussed.