The cathodic deposition of radioactive rare earths has been studied. The experiments establish the existence of a critical current density Imin, below which no deposition takes place. The dependence of Imin on the acid concentration and the stirring rate was examined for nitric acid solutions. The results are in agreement with calculations based on the diffusion layer concept. The addition of inert salts such as Ba(NO3)2 or KNO3 causes a substantial decrease in the deposition rate. Most experiments have been performed with platinum cathodes, but silver and gold are equally applicable. Alcohol in the solution improves the source quality.