Beta-Hydroxyisovaleric acid (also known as 3-hydroxyisovaleric acid or 3HIA) is a normal human metabolite excreted in the urine. It is a byproduct of the leucine degradation pathway. Beta-Hydroxyisovaleric acid serves as a sensitive indicator of marginal biotin deficiency in humans. The variability of the proportion of leucine catabolites excreted as 3HIA suggests substantial population heterogeneity in the metabolic capacity of the 3HIA-carnitine detoxification pathway. In addition, was shown that in type II diabetic patients the catabolism of leucine was accelerated even in the absence of ketosis and that the urinary beta-hydroxyisovaleric acid concentration was a useful marker of short-term metabolic control in these patients.