Tissue typing was performed on 1000 unrelated multiple sclerosis (MS) patients and 1000 unrelated healthy controls. In addition, segregation analysis of HLA antigens and haplotypes in 36 MS families was done. The following results were observed: HLA-A3 and HLA-B7 were found significantly more often in MS individuals; haplotype HLA-A3-B7 was observed significantly more often in MS patients than in healthy indiciduals of the same population; the association between HLA-A3 and HLA-B7 was signigicantly stronger in MS patients than in controls; the haplotype HLA-A3-B7 shows a common segregation with the disease multiple sclerosis (p = 0.02); and the hypothetical "MS-disease-susceptibility-gene" may be located between the second locus and the HLA region and the MLC (mixed lymphocyte culture)-histocompatibility-determinant-region on chromosome No. 6.