Deuterium labelling of the succinimide ring of N-(3,5-dichlorophenyl) succinimide (NDPS) markedly reduced the acute nephrotoxicity produced by NDPS administration to Fischer 344 rats. Administration of the deuterium-labelled derivative, NDPS-d4, to male Fischer 344 rats failed to produce the marked diuresis, increased proteinuria, glucosuria, hematuria, elevated blood urea nitrogen (BUN) concentration and kidney weight, decreased basal p-aminohippurate (PAH) accumulation, and proximal tubular necrosis which are characteristic of NDPS-induced nephrotoxicity. However, lactate-stimulated PAH and tetraethylammonium (TEA) accumulation were decreased by NDPS-d4 (1.0 mmol/kg). The lack of nephrotoxicity produced by NDPS-d4 suggests that oxidation at the carbon-carbon bridge of the succinimide ring is an important biotransformation step in the generation of the nephrotoxic species of NDPS.