Papillomata in association with the trichostrongyle, Nochtia nochti Travassos and Vogelsang, 1929 were encountered in the stomachs of 16 of 48 stumptail macaques (Macaca speciosa) from Thailand examined at necropsy. The gross and histological features of the papillomata are described. The tumors were found in the prepyloric region of the stomach, showed no evidence of malignancy, and appeared to represent a reaction of the gastric mucosa to the presence of either the worms or their eggs. The tumors appear to be more common in male monkeys than in females. In experiments on the toxicity of pesticides in stumptail macaques (Macaca speciosa) im- ported from Thailand, incidental papillomata in association with a parasitic nematode were encountered in the stomachs of a large propor- tion of the animals examined at autopsy. Of 48 monkeys examined (24 males, 24 females), 16 (33%) possessed gastric papillomata (13 males, 3 females). Gross findings: The tumors were situated in