The activity of glycerol kinase is found widely in nature. In microorganisms GK makes possible the utilization of glycerol as a carbon source. In mammals the enzyme represents a juncture of sugar and fat metabolism; The enzyme is important to the clinical chemist in the determination of glycerol. GK is also useful in the assay of glyceraldehydes and dihydroxyacetone following their quantitative reduction to glycerol with sodium borohydride.