A massive infection with what is apparently the same species was discovered in a young male Gorilla gorilla gorilla (Savage and Wyman) which died in New York. At death the animal weighed 30.8 pounds and was probably about two years old. It had been brought by airplane from Africa on February 7, 1949, and although it came from the Congo region the locality where it was taken is uncertain. The animal was ill on arrival and shortly thereafter one of us, (L. J. G.) veterinarian of the New York Zoological Society, was called for medical advice and treatment. Its temperature fluctuated between 99 and 102 degrees F.; there were recurrent intestinal disturbances, anorexia, intermittent diarrhea and constipation. At times there were periods of two to four days in which there were no bowel movements. The fingernails had transverse bands of roughened areas, suggesting previous nutritional deficiencies or febrile conditions. Neither anemia or jaundice was noted. One eyelid was injected with one-tenth cc. of 1 percent P.P.D. tuberculin; there was an immediate reaction. An edematous swelling of the lid completely closed the eye in a few minutes, but totally subsided within five hours. No tubercular lesions were observed at autopsy and the significance of the reaction is obscure. Several fecal examinations were made; hookworm eggs were present in large numbers but no trematode eggs were observed. To remove the hookworms, two treatments with tetrachlorethylene were administered but ova persisted in the stools. After the second treatment, diarrhea developed and the mucus contained large numbers of amoebae. Administration of carbarsone had no apparent effect on the amoebae; the dysentery continued and emetine hydrochloride was given. This treatment also proved ineffective; the stools became bloody and were unformed during the subsequent life of the animal. It failed to give the expected response to medication or to symptomatic and supportive measures. During a six week period it lost about four pounds and died of terminal pneumonia on April 2, 1949. Autopsy of the gorilla was begun within three hours after death. The carcass showed no gross lesions other than early stages of lobar pneumonia, but the hepatic and especially the pancreatic ducts were filled with enormous numbers of small trematodes. Examination of the rectal contents revealed a few trematode eggs, but the number was not at all commensurate with the intensity of the infection. A piece of pancreas about 10 by 10 by 15 mm. was teased to bits in a Petri dish containing Ringer's solution. The worms were fixed and counted; 1028 specimens were present. Pieces of the liver and pancreas were removed, fixed and cut in serial