Seventy-eight patients with inflammatory bowel disease (35 with Crohn's disease and 43 with ulcerative colitis) and a control population of 36 children without organic disease were surveyed to determine the frequency of symptoms compatible with cow's milk-protein sensitivity during infancy. The incidence of a history compatible with cow's milk sensitivity was 8.5% (3/35) in patients with Crohn's disease and 2.8% (1/36) in controls. Patients with ulcerative colitis had a significantly greater prevalence of symptoms, compared with the other patient groups (20.9%, 9/43; p less than 0.03). In addition, patients with a history of cow's milk allergy, who subsequently developed ulcerative colitis, did so at an earlier age (6.68 +/- 2.05 yr vs. 10.62 +/- 0.74 yr: p less than 0.02) than those without a history of cow's milk sensitivity. Thus, there appears to be a potential relationship between early cow's milk sensitivity and the development of ulcerative colitis.