The biosorption of chromium(VI) ions from aqueous solutions on dried vegetative cell and spore-crystal mixture of Bacillus thuringiensis var. thuringiensis was tested using the batch method as a function of pH, initial metal ion concentration and temperature. The optimum adsorption pH value observed for chromium(VI) ions was 2.0. At the optimal conditions, metal ion uptake has rised with increasing initial metal ion concentration. Chromium(VI) ions uptake of B. thuringiensis' spore-crystal mixture at 250 mg 1(-') was 24.1%, whereas its vegetative cell metal uptake was 18.0%. Chromium(VI) biosorption experiments were carried out at three different temperatures, 15, 25 and 35 degrees C. The best temperature for biosorption was 25 degrees C. Scatchard plot analysis were used to obtain more compact information about the interaction between chromium(VI) ions and biosorbents. The plot results are further studied to determine if they fit Langmuir and Freundlich models. Scatchard analysis of the equilibrium binding data for chromium(VI) ions on vegetative cell and spore-crystal mixture of B. thuringiensis gave rise to a linear plot, indicating that the Langmuir model could be applied. The adsorption data with respect to the metal provided an excellent fit to both Langmuir and Freundlich isotherms. (c) 2004 Elsevier Ltd. All rights reserved.