Cellular fluorochromes, pyridine nucleotides (PN), and flavoproteins (Fp) reflect the redox state of the cytoplasmic space and mitochondria of the intact cells and tissues and afford a direct readout of essential parameters of cell metabolism. A time sharing fluorometer which alternates every 8 msec the overlapping emission and excitation wavelengths of both fluorochromes enables nearly simultaneous recording of the two components. From a spot of several millimeters in diameter an adequate signal‐to‐noise ratio can be obtained at a response time of less than 0.1 sec. In conjunction with the regenerative flow apparatus, the fluorescence of the components can be recorded in times down to 20 msec. Applicability to reaction kinetics in perfused organs and in suspensions of mitochondria as well as to other systems with double fluorescence labels is indicated.