The objective of this investigation was to characterize the acute and short- and long-term toxic potency of orally administered 1,2-dichloropropane (DCP). In the acute and short-term studies, male rats of 250-300 g were gavaged with 0, 100, 250, 500, or 1000 mg DCP/kg in corn oil once daily for up to 10 consecutive days. Although ingestion of DCP caused body weight loss and CNS depression, few other toxic effects were manifest 24 hr after a single dose of the chemical. Morphological changes were limited to liver centrilobular cells in 500 and 1000 mg/kg rats. Similarly, elevated activity of some serum enzymes occurred only at these two highest dose levels. Hepatic nonprotein sulfhydryl (NPS) levels were decreased and renal NPS levels increased at 24 hr. In the short-term study resistance developed to DCP hepatotoxicity over the 10 consecutive days of exposure, as reflected by progressively lower serum enzyme levels and by decreases in the severity and incidence of toxic hepatitis and periportal vacuolization. Nucleolar enlargement in hepatocytes, however, was observed at all dosage levels at 5 and 10 days. There were a number of manifestations of hemolytic anemia, including erythrophagocytosis in the liver, splenic hemosiderosis and hyperplasia of erythropoietic elements of the red pulp, renal tubular cell hemosiderosis, and hyperbilirubinemia. Urinalyses and histopathology revealed no evidence of nephrotoxicity. In the long-term study, male rats initially weighing 180-200 g were gavaged five times weekly for up to 13 weeks with 0, 100, 250, 500, or 750 mg DCP/kg. As over one-half the 750 mg/kg group died within 10 days, the survivors were sacrificed. Histopathological changes in the 750 mg/kg animals included mild hepatitis and splenic hemosiderosis, as well as adrenal medullary vacuolization and cortical lipidosis, testicular degeneration and a reduction in sperm, and increased number of degenerate spermatogonia in the epididymis in some members of the group. Similar testicular and epididymal degenerative change also were observed in some 500 mg/kg animals after 13 weeks of dosing. There was a progressive increase in the number of deaths in the 500 mg/kg group, such that more than 50% were dead by 13 weeks. No deaths occurred in the 100 or 250 mg/kg groups. The DCP dosage regimen also produced a dose-dependent decrease in body weight gain. DCP exhibited very limited hepatotoxic potential and no apparent nephrotoxic potential in the long-term study. Slight elevations in serum ornithine-carbamyltransferase activity, periportal vacuolization, and active fibroplasia in the liver were seen in the 500 mg/kg animals.