Previous studies demonstrated that chloroform given by oral gavage in corn oil caused an increased incidence of liver tumors in male and female mice and kidney tumors in male rats, while administration in drinking water resulted in an increased tumor incidence only in the kidneys of the male rats. The tumorigenicity of this nongenotoxic agent has been postulated to be linked with cytolethality and cell proliferation. This study examined the organ-specific toxicity of acute doses of chloroform. Male F-344 rats were given chloroform by gavage in corn oil at the bioassay doses of chloroform of 0 and 180 mg/kg body wt as well as 34 and 477 mg/kg and necropsied 24 hr later. Additional rats were given a single dose of 180 mg chloroform/kg and administered bromodeoxyuridine (BRDU) 2 hr prior to necropsy at 0.5, 1, 2, 4, and 8 days after chloroform treatment. Female B6C3F1 mice were given chloroform by gavage at the bioassay doses of 0, 238, and 477 mg/kg as well as 34 mg/kg and necropsied at 24 hr after treatment. Additional mice were given a single dose of 350 mg chloroform/kg, labeled with BRDU, and necropsied at 0.5, 1, 2, 4, and 8 days after treatment. The kidneys of male rats administered 34, 180, and 477 mg chloroform/kg exhibited mild to severe proximal tubular necrosis in a dose-dependent manner. A 20-fold increase in the labeling index (LI, the percentage of nuclei in S-phase) in the proximal tubule cells was observed 2 days after treatment with the bioassay dose of 180 mg/kg. The livers of male rats exhibited only slight to moderate multifocal centrilobular necrosis at 180 and 477 mg/kg. A 10-fold increase in the LI was observed in the liver of male rats given 477 mg/kg, but no increase was observed at the bioassay dose of 180 mg/kg. In contrast to male rats, female mice developed a dose-dependent centrilobular hepatic necrosis at 238 and 477 mg/kg. No renal lesions were observed in female mice at any dose. A peak increase in LI of 38-fold was observed in hepatocytes in the livers of female mice 2 days after treatment with 350 mg chloroform/kg, with only a 2-fold increase in LI observed in the kidneys. These data indicate that acute chloroform-induced cytolethality leads to increased cell proliferation and that the organ-specific pattern of toxicity is the same as the organ-specific pattern of tumor formation.(ABSTRACT TRUNCATED AT 400 WORDS)