To look for possible HLA linkage in familial Crohn's disease, HLA haplotype segregation patterns were determined in 70 members of five kindreds, each having 2 or more patients with Crohn's disease (total number: 13 with Crohn's disease, 1 with ulcerative colitis). Concordant segregation of HLA haplotypes and disease was not observed. Study of HLA A and B locus phenotypes in 64 additional patients with documented Crohn's disease failed to show any significant disease association. We conclude that in these kindreds, HLA linkage does not account for the familial susceptibiltiy to Crohn's disease and that HLA A and B locus antigens are not associated with Crohn's disease.