The biosorption of cadmium(II) ions to C. vulgaris studied in a batch system with respect to the temperature, initial pH and initial metal ion concentration. The algal biomass exhibited the highest cadmium(II) uptake capacity at 20 degreesC, at the initial pH value of 4.0 and at the initial cadmium(II) ion concentration of 200 mg l(-1). Biosorption capacity decreased from 85.3 to 51.2 mg g(-1) with an increase in temperature from 20 to 50 degreesC at this initial cadmium(II) concentration. Freundlich and Langmuir isotherm models were tried to represent the equilibrium data of cadmium(II) biosorption depending on temperature. Equilibrium data fitted very well to both the models in the studied concentration range of cadmium(II) ions at all the temperatures studied. The pseudo first- and pseudo second-order kinetic models were also applied to experimental data assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled. The results showed that cadmium(II) uptake process followed the second-order rate expression and adsorption rate constants decreased with increasing temperature. Using the second-order kinetic constants, the activation energy of biosorption was also evaluated.