The combined effects of trapping of resonance radiation of a more abundant isotope of a gas or vapor (leading to a preferential ionization of the more abundant isotope) and cataphoresis (forcing the preferentially ionized isotope towards the cathode) will be shown to result in an enriched deposition of the less abundant isotope in the anode region of a dc discharge tube. Large isotope enrichment factors and high efficiencies appear to be possible for initially low‐abundance isotopes.