The cysteine conjugates of the nephrotoxins hexachlorobutadiene (HCBD), tetrafluoroethylene (TFE) and hexafluoropropene (HFP), together with those of trichloroethylene and perchloroethylene, have been chemically synthesized and a relationship determined between their structures and their nephrotoxicity and mutagenicity in vitro. All of the conjugates had a marked effect on the uptake of both the organic anion p-aminohippuric acid (PAH) and the cation tetraethylammonium bromide (TEA) into rat kidney slices, suggesting activation of the conjugates in the slices to a toxic species which interferes with ion transport. This observation is consistent with the known nephrotoxicity of HCBD, TFE and HFP in vivo. Each of the conjugates was found to be metabolised by rat kidney slices and by semi-purified rat kidney beta-lyase to pyruvate, ammonia and an unidentified reactive metabolite. When semi-purified beta-lyase was used stoichiometric amounts of pyruvate and ammonia were produced. Although all of the conjugates were activated by beta-lyase and had a similar effect on ion transport their mutagenicity differed markedly. The conjugates of HCBD, trichloroethylene and perchloroethylene were mutagenic in the Ames bacterial mutation assay when activated by rat kidney S9. Metabolic cofactors were not required suggesting that activation was due to the enzyme beta-lyase. In the same assay the conjugates of TFE and HFP were not mutagenic either in the presence or absence of rat kidney S9 and cofactors. With a limited number of cysteine conjugates a clear distinction has been identified between the conjugates of chloroalkenes which were were similarly nephrotoxic but were not mutagenic. The mutagenicity of the cysteine conjugate of HCBD is consistent with the known renal carcinogenicity of this chemical.