Nephrotoxicity of some aromatic nitro-amino compounds were evaluated by urinary enzyme activities and renal histopathological changes. Male Fischer 344 rats were intraperitoneally injected with aniline, p-aminophenol, acetyl-p-aminophenol, p-chloroaniline, p-chloronitrobenzene, p-anisidine, or p-nitroaniline at 1.0 mmol/kg. In the rats injected with p-aminophenol, necrosis of renal tubular epithelial cells and remarkable elevation of urinary N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyltranspeptidase (gamma-GTP) activities were observed. Injection with p-chloroaniline caused significant elevation of the urinary NAG and gamma-GTP activities. p-Anisidine and p-nitroaniline induced swelling of the tubular epithelial cells and a significant elevation in urinary NAG activities in rats, which was also caused by p-chloronitrobenzene. However, administration of aniline or acetyl-p-aminophenol did not change either the urinary enzymes or renal histopathology. These results indicate that p-aminophenol is a highly nephrotoxic substance, and that nephrotoxicity of p-chloroaniline, p-chloronitrobenzene, p-anisidine and p-nitroaniline exceed that of acetyl-p-aminophenol which has been known to cause a renal damage.