Epitaxial PbSe layers were electrodeposited onto InP(111) single crystals, from solutions containing Pb2+ and Cd2+ ions, the latter being largely in excess. It is demonstrated that underpotential deposition of Pb and Cd takes place on InP and PbSe epitaxial electrodeposits. Cd acts by inhibiting superficial sites and is incorporated both at the InP/PbSe interface (2-4%) but also in the bulk of the PbSe layers (1%). The cadmium concentration is maintained at a low level by a chemical displacement of Cd-0 by Pb2+. (C) 2003 The Electrochemical Society.