L-Cysteine increased gold-cyanide biosorption by protonated Bacillus subtilis, Penicillium chrysogenum and Sargassum fluitans biomass. At pH 2, the maximum Au uptakes were 20.5 mu mol g(-1), 14.2 mu mol g(-1) and 4.7 mu mol g(-1) of Au, respectively, approximately 148-250% of the biosorption performance in the absence of cysteine. Au biosorption mainly involved anionic AuCN2- species adsorbed by ionizable functional groups on cysteine-loaded biomass carrying a positive charge when protonated [(biomass-cysteine-H+)-(AuCN2-)]. Deposited gold could be eluted from Au-loaded biomass at pH 3-5. The elution efficiencies were higher than 92% at pH 5.0 with the Solid-to-Liquid ratio, S/L, = 4. Increasing solution ionic strength (NaNO)(3) decreased Au uptake. FTIR analyses indicated that the main. functional groups involved in gold biosorption in the presence of L-cysteine are probably N-, S-and O-containing groups. The present results confirm that certain waste microbial biomaterials are capable of effectively removing and concentrating gold from solutions containing residual cyanide if applied under appropriate conditions.