Several year's ago, Truelove1 dramatically documented a clinical relationship between cow's milk and some cases of ulcerative colitis. Although milk as a causative factor in ulcerative colitis has been sporadically hypothesized since 1926 by Andresen,2 and later by Mackie3 and Rowe,4 this view was founded on a clinical impression of marked improvement when cow's milk was totally excluded. The crucial test performed by Truelove was the reintroduction of milk into the diet of such patients in remission, precipitating within several days or weeks a frank relapse of ulcerative colitis. He pointed out that the likelihood of relapse by chance alone was less than one in a thousand. His subsequent work,5 confirmed by others,6,7 demonstrated the significant presence of higher titers of antibodies to cow's milk proteins at some time during the illness. The lack of correlation of the antibody levels to the various clinical