Biosorption of Reactive Black 5 (RB 5) dye onto dried Penicillium restrictum biomass was studied with respect to pH, contact time, biosorbent and dye concentrations. The effect of temperature on the biosorption efficiency was also carried out and the kinetic parameters were determined. Optimum initial pH, equilibrium time and biomass concentration for RB 5 dye were found to be 1.0, 75 min and 0.4 g dm-3 at 20 degrees C, respectively. The maximum biosorption capacities (q(max),) of RB 5 dye onto dried P restrictum biomass were 98.33 and 112.50 mg (g biomass)(-1) at 175 mg dm(-3) initial dye concentration at 20 and 50 degrees C, respectively, and it was 142.04 mg (g biomass)(-1) at 200mg dm(-3) initial dye concentration at 35 degrees C. The results indicate that the biosorption process obeys a pseudo-second-order kinetic model. (C) 2006 Elsevier B.V. All rights reserved.