BACKGROUND: To investigate the relationship between malondialdehyde in renal cortex and Urinary NAG activity of rats exposed to cadmium. METHODS: Rats were treated with a single intraperitoneal injection of cadmium (as CdCl2, 1 mg/kg) for cadmium-treated group and 24-hour urine were obtained prior to sacrifice on days 1, 2, 4, 8 and 16 (N=10 per each group), respectively. The concentration of malondialdehyde by thiobarbituric acid reaction and cadmium were measured in the homogenates of renal cortex. Nephrotoxocity indices such as N-acetyl--D-glucosaminidase (NAG) activity, total protein, and 24 hours urine volume, and cadmium concentration were measured in the urine. RESULT: The cadmium injection caused significant increase of cadmium concentration in the renal cortex on days 1 and 2, and in urine on days 1, 2 and 4. NAG activity and total protein concentration in urine were significantly increased on days 1, 2 and 4, and on days 1, 4 and 8, respectively. The peak values of NAG activity and total protein in urine were observed on days 1 and 4, respectively. Significant decrease of 24 hours urinary volume was induced on day 1. These results indicated that cadmium induced acute nephrotoxicity in the rats. Urinary NAG activity was changed earlier and at a higher rate than urinary total protein, which suggest that NAG activity is a more sensitive biological index in terms of early diagnosis of cadmium-induced nephrotoxicity. Renal MDA concentration was significantly increased on day 2 and on day 4, and on day 8, MDA concentration and nephrotoxicity indices except urinary total protein were returned to control level. CONCLUSION: Based on the results obtained as above, it was concluded that the malondialdehyde in renal cortex, product of lipid peroxidation was related with the changes of urinary NAG activity indicating nephrotoxic injury.