In contrast to NAD(P)H data, metabolic-FLIM data derived from FAD images are often inconclusive. It has long been suspected that FAD data are biased by a fluorescence decay component from FMN. We therefore checked for possible traces of FMN fluorescence in FLIM data recorded by our DCS-120 metabolic FLIM system. Indeed, we found a decay component with a lifetime around of 4.3 to5 5.5 ns which cannot be attributed to FAD but very well to FMN. The amplitude of the FMN component was 3.9% to 5% in normal cells and 8.8% to 10 % in cancer cells. We are finding the FMN component both in data from larger ROIs with high photon numbers and in pixel data with large binning factors. Please see figures below. The presence of a decay component from FMN may have implications to the use of FAD data for cancer diagnosis, especially if the the amplitude ratio, a1/a2 or the FLIRR ratio is used as cancer indicators. Certainly, an amplitude contribution of 3.8 % or even 8.84 % does not render the a1/a2 ratio or the FLIRR ratio useless. It can, however, introduce unpredictable shifts in these parameters. Please see Application Note for more information.