The paper presents new data concerning the mechanism of microbiological dissolution of gold. The sign of charges on gold-protein complexes was determined by paper electrophoresis. Anion complexes were found to prevail. Free amino groups participate in formation of complexes between gold and amino acids in alkaline medium, and functional groups of amino acid residues in polypeptide groups are involved in formation of complexes with proteins. Formation of complexes between gold and these compounds seems to be due to the Au--N bond.