Groups of 15 males and 15 females Sprague-Dawley rats were given 20 ml of drinking water solution containing either 0.2% heptamethyleneimine hydrochloride or this salt together with 0.2% sodium nitrite, 5 days a week for 28 weeks. Another group of 17 male and 30 female rats was given 0.2% sodium nitrite solution for 104 weeks. Most of the animals given heptamethyleneimine hydrochloride or sodium nitrite alone survived 2 years or more after the beginning of the treatment, and no tumors attributable to the treatment were seen at death; tumors appearing were those of endocrine origin found commonly in untreated controls. In the group receiving the combined treatment, most females were dead at 50 weeks and most males were dead at 80 weeks, 27 of 30 having tumors not seen in either control group. A total of 16 had squamous carcinomas in the lung; 25 had tumors of the oropharynx, tongue, esophagus, and forestomach; and there were a few animals with tumors in the nasal cavity and trachea. The expericment showed that squamous tumors of the lung could be induced by ingestion an amine and sodium nitrite.