Waste biomass Sargassum sp. biosorbed 100% of Cd2+ and 99.4% of Zn2+ from a 3 and 98 mg l(-1) solution (pH 4.5), respectively, at the end of four serial experiments. Of the five desorbents studied in consecutive adsorption/desorption cycles, CaCl2 0.05 M eluted nearly 40% of both metals and decreased the biosorption in only 8% and 17% of Cd2+ and Zn2+, respectively. Although NaOH desorbent improved the heavy metal uptake from the second cycle onwards, it did not elute metals from the pre-loaded biomass.