The nonstoichiometry of lead sulfide was studied and heteroimpurities were introduced electrochemically into highly conducting oxides Bi₃BaO_5.5 and YBa₂Cu₃O_7-x by coulometric titration in a cell with sulfide-conducting solid electrolytes based on CaPr₂S₄ and CaSm₂S₄. The mechanism of defect formation in nonstoichiometric PbS_1-δ was studied.