Rats were exposed to sodium nitrite in food or water at concentrations of 0, 250, 1000, and 2000 parts per million. Lymphoma was increased in all groups fed nitrite; the overall combined incidence was 5.4 percent in 573 control rats and 10.2 percent in 1383 treated rats. The mechanism of cancer induction did not appear to be through the formation of nitrosamines but through a more direct effect of nitrite on the lymphocyte.