Recently, ethylene was reported to be involved in the regulation of Fe(lll)-chelate reducing capacity by cucumber (Cucumis sativus L.) roots. Here, we studied the effect of two ethylene inhibitnrs, aminooxyacetic acid (AOA) and cobalt, on the Fe(lll) reducing capacity in roots of mutant genotypes [El07 pea [Pisum sativum L. (brz, brz)] and chloronerva tomato (Lycopers&on esculentum L.] that exhibit high rates of Fe(lll)-chelate reduction and excessive iron accumulation. The ethylene inhihitors, AOA and cobalt, markedly inhibited Fe(lll)-chelate reducing capacity in roots of both genotypes. Over-expression of root Fe(lll) reductase activity by both mutants appears to be related to ethylene. Possibly, both mutants are genetically defective in their ability to regulate root ethylene production. The large inhibitory effect of both ethylene inhibitors on Fe(lll)-ehelate reducing capacity in roots of the mutant tomato genotype, chloronerva, disputes the contention that the nicotianamine-Fe(ll) complex is the repressior of the gene responsible for Fe(llI)-chelate reductase activity, as previously suggested by others. However, since nicotianamine shares the same biosynthetic precursor as ethylene, i.e. S-adenosyl methionine, nicotianamine may affect Fe(lll)-ehelate reductase activity in dicot and non-grass monoeot roots by influencing ethylene biosynthesis.