The electrochemical behavior of AgBr and CuBr has been studied in a solution consisting of 0.80M KBr and 1.0M Al2Br6 in ethylbenzene. A significant crystallization overpotential is observed for Cu on Pt, while silver exhibits only a marginally small crystallization overpotential. Measurements of the diffusion coefficients by different methods and comparison with earlier results yield values in the range of (1.1-2.9) x 10-6cm2/s (corresponding to Stokes radii of 9-4Å), except for Cu, which yields a value of (10–21) x 10-6cm2/s. These high apparent values are probably due to catalytic decomposition of the solvent caused by the presence of cuprous ions. The relatively high value for the diffusion coefficient of mercuric ions in toluene reported in an earlier publication is probably due to the same effect.