Amino acids L-valine, glycine, DL-alpha-alanine and L-histidine were applied in the ammoniacal thiosulphate leaching of a pyrite concentrate. Amino acids formed more stable complexes with cupric ions than does ammonia, resulting in lower thiosulphate consumption due to reduced interaction between thiosulphate and the copper complexes. Overall gold extraction was largely improved by the addition of amino acids, despite lower initial kinetics. Thiosulphate consumption decreased with an increase in the amino acid concentration. Among the amino acids, L-histidine improved overall gold extraction and reduced the thiosulphate consumption to the greatest extent. (C) 2011 Elsevier Ltd. All rights reserved.