1. 1. Polarographic recordings of 0.001 M solutions of adrenochrome at 3 °C. taken before, during, and after reduction with hydrogenplatinized asbestos over a pH range of 5.61–8.08 indicated that under these conditions a two-electron reversible reduction occurs with a low order of semiquinone formation. In confirmation of previous studies, the reductant was found to be fairly stable above pH 7.0. 2. 2. Measurements of hydrogen uptake by solutions of adrenochrome, prepared by both the iodine and silver oxide oxidation methods, in which reduction was catalyzed by both platinized asbestos and palladinized barium sulfate under the same approximate conditions of temperature, concentration, and pH as above, showed an initial rapid consumption of two atoms of hydrogen per molecule of adrenochrome. The same result was obtained with the similar red compound prepared by the oxidation of epinine. 3. 3. The present results are in agreement with the structures of the adrenochrome redox system originally proposed by Green and Richter. Discordant reports in the current literature are discussed and possible reasons for the discrepancies suggested.