A sequential extraction-radiotracer technique was applied to a sediment core sample collected from lake Biwa (Japan) in order to evaluate relative importance of the fractionated solid components to sorb Zn(II) ions. The core was previously divided into three parts from the surface of the sediment; upper (0-6 cm), middle (6-12 cm) and bottom (12-18 cm). The solid residue after each chemical treatment was collected to perform a sorption experiment by using (65)Zn as a tracer. A difference in the amount of Zn(II) sorption was observed among original samples without any chemical treatments at each depth. The amounts were very small (10(-5) -10(-4) mol Zn(II) 100 g(-1) of dry sample) in all fractions of the sediment. Electrochemical measurements of cadmium and copper ion sorption supported the results from the radiometric sorption experiment. The effects of several potential factors on zinc sorption were investigated. Ion exchange of zinc with protons on the mineral surfaces was a significant cause of the zinc sorption.