Immunoglobulin allotype markers on immunoglobulin G (Gm markers), immunoglobulin A (A2m markers), and kappa light chains (Km markers) were determined in 68 Crohn's disease patients, 39 ulcerative colitis patients, and 1027 healthy controls. Patients and controls were all Caucasians of Northern European origin and not Jewish. The distribution of immunoglobulin heavy-chain (Gm) allotypes differed markedly between Crohn's disease patients and controls. Crohn's disease patients had a significant increase in the frequency of the phenotype Gm(a,x,f;b,g) and the haplotype Gma,x;g. The frequency of Gm phenotypes and haplotypes did not differ significantly between ulcerative colitis patients and controls. Further, there was no significant association between Km markers or A2m markers and inflammatory bowel disease.