The role of biotin as the prosthetic group of the four biotin-dependent carboxylases in higher organisms is well recognized. Based on the roles of these carboxylases in metabolism, the requirement of biotin for cell viability, growth and differentiation was established. Biotin seems to have a role in cell functions other than as the prosthetic group of biotin enzymes. Biotin seems to influence processes such as the proliferation of the mesenchyme, spermatogenesis and song-bird vocalization. A direct effect of biotin, at the transcriptional level, has been shown for the key enzymes of glucose metabolism. Glucokinase, a key glycolytic enzyme, and phosphoenolpyruvate carboxykinase (PEPCK), a key gluconeogenic enzyme, are regulated in opposite directions by biotin in a manner similar to the action of insulin.