The aim of the present study is to analyze the competitive adsorption of cadmium (Cd(II)), nickel (Ni(II)), and zinc (Zn(II)) ions onto rice husk ash (RHA) from ternary metal ion mixtures. RHA is a waste material obtained from the flue gas of the rice husk fired boilers. The equilibrium adsorption data were obtained at different initial concentrations (C(0) = 10 to 100 mg.dm(-3)), 5 h contact time, 30 degrees C temperature, and RHA dosage of 10 mg.dm(-3) at pH = 6. The Freundlich and the Redlich-Peterson models represent the single ion equilibrium adsorption data better than the Langmuir model. The equilibrium metal removal decreases with increasing concentrations of the other metal ions, and the combined action of Cd(II), Ni(II), and Zn(II) ions on RHA is found to be antagonistic. The competitive Sheindorf-Rebuhn-Sheintuch (SRS) model fits the ternary adsorption equilibrium data satisfactorily.