Metallic tin powder injected into Lewis rats caused marked enlargement of draining lymph nodes with prominent hyperplasia of plasma cells. A low level of dietary protein (8%) or deficiency of choline interfered with the cellular proliferation and reduced the size of the nodes by nearly one-third compared to a normal protein diet (20%). A high level of protein in the diet (50%) did not augment the effect of metallic tin powder beyond that achieved by a level usually considered adequate (20%).