Serum antibodies to five cow's milk proteins, alpha-casein, bovine serum albumin (BSA), beta-lactoglobulin A and B (BLG-a, BLG-b) and alpha-lactalbumin (ALA) were investigated in young patients with inflammatory bowel disease, 56 with Crohn's disease (CD), 24 with ulcerative colitis (UC). IgG antibodies against BSA and BLG-a and -b were higher in Crohn's disease patients as compared to those with ulcerative colitis and controls. The IgG anti-BSA were higher in the group of CD patients with higher score of disease activity. Additionally, IgA antibodies to alpha-casein were higher in CD and UC compared to control. These findings may be due to increased uptake of dietary antigens or enhanced immunological response occurring in CD patients.