A double beam fluorescence spectrophotometer has been designed for the analytical control laboratory and for some research applications. It has several modes of operation in addition to double beam, in which the difference in fluorescence between two samples is measured. The design concept (developed by Ohnishi) employs equivalent optical paths for both beams, an optical chopper, and a time sharing electrooptical system. Since it is a true double beam system it may also be used to record the percent transmission spectrum of a sample, which is placed in monochromatic light, as both excitation and emission monochromators are scanned synchronously. For identification of pure samples in dilute solutions a relative quanta excitation spectrum may also be recorded. Some applications for the double beam fluorescence concept are to improve quantitative results by eliminating interference due to scatter and due to unwanted fluorescence peaks, to control product quality by matching two samples of similar characteristics and to assay trace organic compounds.