Male and female Fischer 344 rats and B6C3F1 mice were exposed by inhalation to target concentrations of 0, 5, 20, or 60 ppm (0, 22.7, 90.8, or 272 mg/m3) technical-grade 1,3-dichloropropene (DCPT) 6 hr/day, 5 days/week, for up to 2 years. Ancillary groups of rats and mice were exposed for 6- and 12-month periods. Significant treatment-related nonneoplastic changes following exposure for 2 years were morphological alterations in the nasal tissues of rats exposed to 60 ppm and mice exposed to 20 or 60 ppm DCPT. In addition, mice exposed to 20 or 60 ppm had hyperplasia of the transitional epithelium lining the urinary bladder. Survival of male and female rats and mice exposed to DCPT was similar to that of the corresponding controls. No statistically increased tumor incidence was observed in treated rats. The only neoplastic response observed in mice was an increased incidence of benign lung tumors (bronchioloalveolar adenomas) in male mice exposed to 60 ppm DCPT (22/50 versus 9/50 in controls).