It isimportant for pathologists to search for early signs of disease because they may give clues to etiology and may also be of possible interest to those concerned with treatment. Most authors have regarded oedema and lymphatic dilatation as the earliest morphological lesion of Crohn's disease (Blackburn et al. 1939, Hadfield 1939, Rappaport et al. 1951, Robb-Smith 1971). The earliest macroscopic lesion is probably the type of ulceration described as' aphthoid'(Brooke 1953). These tiny ulcers can be found in mucosa at a distance from more obviously diseased bowel. They vary from tiny, pinheadsized lesions to small, clearly demarcated ulcers with white bases. They will be missed if surgical specimens are not carefully preparedand examined. They are sometimes detected close to the limit of excision of resected specimens of gut and if left behind by the surgeon may well be the pathological basis for recurrent disease. Experience suggests that these early lesions