Administration of N-nitrosodimethylamine (NDMA) to zinc deficient rats intragastrically twice weekly for 8 weeks resulted in the development of forestomach tumors in 63% of treated animals. The tumors were frequently found at the junction between the fore and glandular stomach and were multiple. Smaller numbers of tumors were also present in the more proximal parts of the forestomach. All tumors were squamous papillomas. Similar tumors were not observed in zinc sufficient pair-fed rats given NDMA. These findings showed that NDMA, a non-esophageal and non-forestomach carcinogen in the rat, was tumorigenic in the presence of zinc deficiency.