N-(2,3,4,5,6-pentahydroxylhexyl)-L-cysteine (4) and N,N'-di(2,3,4,5,6-pentahydroxylhexyl)-L-cystine (5) were synthesized. As antagonists of cadmium or lead intoxication, they were found to be effective by oral administration on repeated exposure. The bioassay in vivo indicated that their cadmium-mobilizing potencies are significantly superior to those of N-acetyl-L-cysteine and their lead-mobilizing properties are equivalent to those of DL-penicillamine (DL-PA). The stability constants of the Cd-4 and Cd-5 complexes or Pb-4 and Pb-5 complexes were determined by use of pH titration. The membrane permeability of compounds 4 and 5 was evaluated by transporting across the Caco-2 cell monolayer. The effect of compounds 4 and 5 on the concentrations of essential metal ions in the renal cortex is negligible in comparison with that of the group treated with lead only. The acute toxicity of compounds 4 was tested by oral gavage and the resulting LD50 value for both mice and rats is larger than 10 g kg(-1) bw. The cytogenetic effects of compound 4 were evaluated in the Ames assay, mouse bone marrow micronucleus test, and sperms shape abnormality assay, and all of them show the negative reactions.