ABSTRACT. Serum antibodies to five cow's milk proteins (α-casein, bovine serum albumin, β-lactoglobu-lin A and B, and α-lactalbumin) were investigated in young patients with inflammatory bowel disease (56 Crohn's disease, 24 ulcerative colitis). IgG antibodies against bovine serum albumin, β-lactoglobulin A and β-lactoglobulin B were higher in Crohn's disease patients than in those with ulcerative colitis or the controls. IgG anti-bovine serum albumin antibodies were higher in those Crohn's disease patients who had higher scores of disease activity. Finally, IgA antibodies to α-casein were higher in patients with Crohn's disease and ulcerative colitis when compared to controls. These findings may be due to increased uptake of dietary antigens or enhanced immunological response occurring in Crohn's disease patients.