The carcinogenic activity of orally administered N-bis(2-hydroxypropyl)-nitrosamine (DHPN) in male Wistar rats was evaluated with respect to its dose. DHPN was administered at two doses, 100 ppm and 500 ppm, in the drinking water to rats for 25 to 52 weeks. Tumors developed in the lung, liver, and thyroid of rats receiving 100 ppm DHPN and in the lung, liver thyroid, esophagus, kidney, and urinary bladder of rats receiving 500 ppm DHPN. The principal target organ was the lung in rats receiving either 100 or 500 ppm DHPN, indicating that the carcinogenic action of these doses of DHPN was similar to that of higher doses previously reported[2].