Epidemiological Studies have reported that the formation of renal stones is often observed in workers exposed to cadmium (Cd). Citrate is known to be a protective factor against renal stone formation. We previously reported that direct exposure to high-level cadmium impaired the citrate uptake by the brush border membrane vesicles (BBMV), which may mean that the formation of renal stones from exposure to Cd could be prevented. In the present study, to clarify the mechanism of Cd-induced renal stone formation, the characteristics of BBMV-induced citrate uptake were determined in Cd-intoxicated rats. Cd intoxication was induced by daily subcutaneous injections of CdCl2 at a dose of 2 mg Cd/kg body wt per day for 17 to 20 days. The BBMV were prepared by the divalent cation precipitation method. Citrate uptake was measured by the Millipore rapid membrane filtration technique. The citrate uptake per mg protein was not significantly different between the two groups. The volume of BBMV was significantly reduced (50%) in Cd-intoxicated rats compared with that of control rats. Percentages of the equilibrium value were also significantly inhibited in Cd-intoxicated rats.