Summary: ATP is the primary energy currency of living systems. Virtually all energy requiring processes utilize the chemical energy stored in the phosphate bond of ATP. ATP is formed exclusively in the mitochondria and a variety of genetic diseases can affect ATP formation in the mitochondria. There are a number of commercially available ATP assays which detects femtomoles or less of ATP by measuring luminescence but these kits require specialized luminescence instrumentation and utilize luciferase which can be difficult to maintain in active form. The newly developed ATP Colorimetric and Fluorometric Assay kit is designed to be a robust, simple method which utilizes the phosphorylation of glycerol to generate a product that is easily quantified by colorimetric (λmax = 570 nm) or fluorometric (Ex/Em = 535/587 nm) methods. The assay can detect as low as 50 picomol (1 μM) of ATP in various samples. The kit provides sufficient reagents for 100 assays.