Pyoderma gangrenosum has become well established as a clinical entity since its description in 1930. In cases subsequently reported, chronic ulcerative colitis has frequently been an associated finding. In our own recent experience, chronic ulcerative colitis was present in only 11 of 19 patients with pyoderma gangrenosum, or approximately 60%. However, of the remaining eight patients, four were known to have other intestinal disease and two gave a history of gastrointestinal disturbances. It is well known that the skin of patients with pyoderma gangrenosum is hypersensitive, particularly during the acute phase of the disease. New lesions develop at the sites of injury from skin tests, the injection of vaccine, or even casual trauma. Two patients in this series (Cases 14 and 18) experienced a profound aggravation and generalization of their lesions of pyoderma gangrenosum following the ingestion of potassium iodide administered elsewhere on an earlier