This case relates to a man, 46 years old, who during the last six months was suffering from diarrhoea. He was in a camp and remained there, his complaints not being considered serious. Three weeks before his admission to the hospital, his diarrhoea grew so violent, that he had to stop working and was sent home. At that time the patient was already in a precarious condition, exhausted, dull and exsiccated, and he had watery stools with blood, 10-20 times a day. Apart from a little pain at palpation of the colon, physical examination showed nothing particular. Blood pressure 110/80 mm Hg; Haemoglobin 115%; erythrocytes 6,240,000 per mm3; slight leucocytosis 15,500 per mm3; blood sedimentation 2 mm after one hour, 6 mm after two hours (Westergren). Serological and bacteriological reactions to typhoid, paratyphoid A and B and dysentery were negative. In spite of the abundant supply of fluids, administered subcutaneously as well as intravenously, the man succumbed the fourth day after arrival in the infirmary with symptoms of increasing uraemia. The last two days of his life the patient was incontinent, evacuating watery stools at every change of attitude. Post mortem: The mucosa of rectum, colon and cecum showed a thin greenish coating on the swollen folds and more or less transverse red-violet spots up to 1 cm wide, with whimsically formed yellow ulcers. The ulcers were often situated near the mesenteric insertion and were frequently arranged in groups or rows. The ulcers contained thin feculent matter with bloodclots. The appendix showed nothing particular. About midway in the ileum there were two ulcers of 1.3 by 0.7 cm and somewhat lower down four little ones, all with a red-violet bottom. Histological examination revealed a gangrenous ulceration in rectum, colon and ileum with numerous worms penetrating as far as submucosa and subserosa. The pathologist's (Dr. M. Straub, Rotterdam) diagnosis said: acute ulcerative exacerbation of a chronic entero-colitis throughout rectum and colon, and some ulcers in the ileum, due to oxyuriasis. On account of the finding of nematodes, samples of the colon, rectum, liver, spleen and kidney, fixed in formalin were sent to the Institute for Tropical Hygiene in Amsterdam. Small pieces of the bowels were teased under a binocular and we succeeded in extirpating some hundreds of worms, many of them undamaged. Pieces of the enteric wall with a square area of I-1 cm2 were divided lengthwise so that one part consisted of mucosa, submucosa and muscularis circularis and the other part of muscularis longitudinalis, transmuscular fat and serosa as far as the bowels were covered with it. In this way it became clear which worms were inside the tunica muscularis and which were outside. Eight pieces of the colon and eleven pieces of the rectum were examined, from macroscopically sound parts as well as from ulcers. In all parts save one we discovered worms in varying quantities. The free worms