The ability of selected metals (Ag, Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Tl and V) to displace Zn from Zn-metallothionein (Zn-MT) was quantitated. Of the metals tested Cd had the highest affinity for MT, with 1.33 microM displacing 50% of the 65Zn bound to MT (EC50), followed by Pb (1.46 microM), Cu (1.93 microM), Hg (3.93 microM), Zn (8.06 microM), Ag (10.4 microM), Ni (474 microM) and Co (880 microM). As, Ca and Mo had a limited ability to displace Zn from MT while Al, Cr, Fe, Mg, Mn, Tl and V had no effect on Zn binding even at 1.0 mM.