Campylobacter fetus subspecies coli was isolated from the small intestines of 17 piglets less than six weeks of age submitted for diagnosis. Sixteen of these animals had enteritis and in five of them no other probable bacterial cause of the enteric lesions was identified. Changes including congestion of the small intestinal mucosa, reduction in the height of the villi, thickening of the terminal ileum and histological evidence for inflammatory change in the small intestine were seen at post mortem examination. C f subsp coli was also isolated from the large intestinal mucosa of all the infected pits. In a further study, the organism was recovered from the colonic mucosa of 10 weaned animals treated for experimental swine dysentery. Two of these animals which had had a persistent mucoid diarrhoea were found to have large intestinal lesions resembling those of mild swine dysentery. No spirochaetes could be demonstrated in or isolated from the lesions seen in these two animals or from the other eight. The possibility that C f subsp coli may be a cause of enteritis in unweaned piglets and produce changes primarily in the small intestine is discussed. Evidence that C f subsp coli may cause large intestinal lesions in weaned pigs under certain circumstances is also discussed.