Sorption and cosorption of lead (Pb(II)) and methylene blue (MB) in aqueous solutions on low-cost biosorbents made from chemically modified agricultural by-products was investigated. Modified cotton exhibited the highest adsorption capacity for Pb(II), while modified cotton and peanut hull had higher equilibrium adsorption capacity of MB than the other biosorbents. Different chemical modification methods of hickory resulted in no great variation on the equilibrium adsorption capacity of Pb(II) and MB except for the one treated with alkali. Simultaneous sorption of Pb(II) and MB on the biosorbents showed Pb(II) to be preferentially adsorbed at higher Pb(II)-to-MB molar ratios in solution except for modified peanut hull. The equilibrium Pb adsorption contents decreased with the increasing pre-loading of MB and vice versa, suggesting the competitive rather than synergistic adsorption of the two contaminants on the biosorbents. (C) 2014 Elsevier Ltd. All rights reserved.