The purpose of this review is to summarize articles about biotin labeling of blood components. Biotin (vitamin H) is present in plasma and serves as a coenzyme for several intracellular carboxylase enzymes of intermediary metabolism. Biotin is not normally found on the cell surface, biotin labeling is stable in vivo and does not affect cell survival. This labeling technique of erythrocytes was performed in animals and also in humans; it allows the determination of red-cell volume and red-cell survival without radioactivity and thus is applicable in children and pregnant women. Transfusion of biotinylated platelets to animals and humans did not cause any adverse events, even when healthy volunteers were rechallenged by transfusion of biotinylated platelets. Negative effects of biotinylated cells have been minimal in vivo, and one of the great advantages of this labeling technique is its low toxicity. However, further studies will require close attention to possible immunological consequences.