Serum immunoglobulin A, and G subclasses were measured in patients with ulcerative colitis, Crohn's disease, and in normal controls. Significant differences were noted in elevated total gamma globulin in both disease groups: in elevated IgG1 in ulcerative colitis and elevated IgG2 in patients with Crohn's disease. These differences were not significantly related to disease activity in either disease although higher levels were observed in those with moderate and severe disease.