Heavy metals are known to induce Fe chlorosis in different plant species. Heavy-metal-induced chlorosis is generally correlated with low plant Fe contents, suggesting effects of heavy metals on Fe mobilization and uptake. Under Fe-deficient conditions, dicotyledonous plants enhance root Fe(lll) reductase activity, thus increasing the capacity to reduce Fe(MI) to Fe(ll), the form in which roots absorb Fe. We studied the effect of several heavy metals (Mn, Pb, Zn, Mo, Ni, Cu, and Cd) on the induction of enhanced root Fe(lll) reductase by 11-d-old Fe-deficient cucumber [Cucumis sativus L. cv. Ashley). The effect of these heavy metals on the function of the induced Fe(lll) reductase was also investigated. Results showed that some heavy metals can inhibit both the induction and function of root Fe(lll) reductase. Ni, at 20//M, and Cu and Cd, at 5 fiM concentration or higher, severely inhibited the induction of root Fe(lll) reductase while Mn, Pb, Zn, and Mo had little effect, even at concentrations higher than 20 //M. Function of the induced root Fe(lll) reductase only was negatively affected by Cu and Ni.