The ambient temperature adsorption of the metal cations Zn2+, Cu2+ and Pb2+ on Pinus pinaster bark pretreated with acidified formaldehyde solution, and particularly the influences of the pretreatment conditions and of the pH of the cation solution on the adsorption capacity of the bark, were investigated. The equilibrium data were satisfactorily fitted by Freundlich isotherms. The bark was an excellent adsorbent, suitable for removal of toxic ions from wastewater with efficiency comparable to commercially available adsorbents, but at a reduced cost.