Our previous studies have shown that major metabolites of nitrobenzene in bovine and fowl were p-nitrophenol, p-aminophenol, and p-nitroaniline. There are few reports about the subacute toxicity of the three metabolites. The aim of this study was to investigate the subacute toxicity of these compounds. A suspension containing three metabolites at 50, 25, and 5 mg kg(-1) body weight was administrated introgastrically to Sprague-Dawley rats of both sexes for 4 weeks. All four groups survived to the end of the 4-week treatment period. Compared to the control group, there was a significant difference in body-weight increases in rats administered nitrobenzene metabolites at 50 and 25 mg kg(-1) (P < 0.01). ALT, AST, ALP, T-CHO, TP, albumin, and creatinine were significantly increased in the 50-mg kg(-1) group and tended to increase in the 25-mg kg(-1) group, compared with controls. There was no significant difference in glucose between treatment groups and controls. RBC counts and concentration of Hb decreased significantly in the 50- and 25-mg kg(-1) groups, compared with controls, whereas WBC and Ret counts increased in the 50- and 25-mg kg(-1) groups and LYM only in the 50-mg kg(-1) group. There were no significant differences in MONO and neutrophil counts, compared with controls. Methemoglobin concentrations were significantly increased on day 21 of treatment in the 50-mg kg(-1) group and on day 28 in the 25- and 50-mg kg(-1) groups. The subacute toxicity was characterized by lesions affecting the liver, kidneys, spleen, cerebellum, and hematopoietic system.