Assay of nicotinamide nucleotides is of continual interest in the studies of energy transforming and redox state of cells or tissues. BioVision's NADH/NAD Quantification Kit provides a convenient tool for sensitive detection of the intracellular nucleotides: NADH, NAD and their ratio. The NAD Cycling Enzyme Mix in the kit specifically recognizes NADH/NAD in an enzyme cycling reaction. There is no requirement to purify NADH/NAD from samples. The reaction specifically detects NADH and NAD, but not NADP nor NADPH. The enzyme cycling reaction significantly increases the detection sensitivity and specificity. NADt (NAD and NADH) or NADH can be easily quantified by comparing with standard NADH.