Dry biomass of Spirulina platensis re-hydrated for 48 h was employed as a biosorbent in tests of cadmium(H) removal from water. Various concentrations of biomass (from 1 to 4 g l(-1)) and metal (from 100 to 800 mg l(-1)) were tested. Low biomass levels (X-o <= 2 g l(-1)) ensured metal removal up to 98% only at Cd-0 = 100 and 200 mg l(-1), while X-o >= 2.0 g l(-1) were needed at Cd-0 = 400 mg l(-1) to achieve satisfactory results. Whereas X-o = 4.0 g l(-1) was effective to remove up to Cd-0 = 500 mg l(-1), a further increase in metal concentration (Cd-0 = 600 and 800 mg l(-1)) led to progressive worsening of the system performance. At a given biomass levels, the kinetics of the process was better at low Cd2+ concentrations, while, raising the adsorbent level from 1.0 to 2.0 g l(-1) and then to 4.0 g l(-1), the rate constant of biosorption increased by about one order of magnitude in both cases and the adsorption capacity of the system progressively decreased from 357 to 149 mg g(-1). (C) 2007 Elsevier Ltd. All rights reserved.