Infection of pigs by the whipworm (Trichuris suis) resulted in profuse diarrhea on postinfection days 17 to 21. Anorexia, retardation of growth, dehydration, and emaciation were observed in infected pigs. Scanning electron micrography showed nematodes embedded in the mucosa of the cecum and colon, with resultant disruption of the mucosa. Infected pigs had decreased values of albumin, amylase, calcium and creatine phosphokinase, but increased values of alpha-, beta-, and gamma- globulins, total iron-binding capacity, copper, potassium, uric acid, and aspartate aminotransferase.