A study of the electrolysis of PbS in molten PbCl2 showed cathode efficiencies which increased with current density at fixed sulphide concentrations, and decreased with increasing sulphide concentration at fixed current densities. The anodically produced sulphur dissolved rapidly in the melt, the rate increasing with temperature and sulphide concentration. Experiments with diaphragm cells, made to determine the relative effects that dissolution of lead and sulphur have on the cathodic current efficiency, demonstrated that dissolution of sulphur was the major contributor to the lowering in efficiency.