With increasing amounts of electroinactive amitriptyline, each of the three chlordiazepoxide reduction waves shifted to more cathodic half-wave potentials and decreased in limiting current. The shift was most pronounced up the 1:1 mole ratio but continued up to ratios of 200:1. This behavior was observed in several supporting electrolytes and was not due to change in pH since this factor was maintained constant as the amitriptyline concentration was increased. Shifts in E1/2 and reductions in limiting current may arise in several ways, such as complex formation between the two drugs or adsorption of the amitriptyline onto the surface of the dropping mercury electrode hindering chlordiazepoxide reduction. Most data point to adsorption as the cause.