An automated luminometer was designed and constructed to facilitate the investigation of reaction conditions and quantitation of the chemiluminescence observed during the oxidation of NADH by horseradish peroxidase in the presence of eosin. The luminometer design incorporates a computer controlled reagent induction system, pulse counting detector and real time display of luminescence profiles. Each of the major reaction conditions was studied individually to determine the most favorable conditions for the analytical application of this reaction. In addition, this chemiluminescent reaction was studied to determine if the luminescing species is recycled. If this were the case it would provide the first essential step necessary for the future design of a chemiluminescent probe that could be reusable or be used for continuous monitoring. During the course of this investigation it was observed that the luminescing species, eosin, was being bleached. A number of experiments were undertaken to determine the nature of the bleaching process. Those steps which suppressed the bleaching process, unfortunately, also suppressed the emission process. Despite the fact that this reaction does not appear to recycle the luminescing species, it does provide a chemiluminescent method for the determination of NADH over the range 5x10⁻⁶ M to 5x10⁻⁴ M. This chemiluminescent reaction has also been coupled to several enzyme systems, which reduce NAD⁺ to NADH, in order to obtain a chemiluminescent signal proportional to the substrate concentration. / Ph. D.