The NcoI polymorphism of the HSP70-Hom gene was investigated in the Finnish population and in two HLA-B27-associated autoimmune diseases. The two HSP70-Hom alleles were shown to be strongly associated to some specific HLA-B/DR haplotypes in random Finnish population and the segregation of the alleles as a part of these haplotypes was confirmed in 18 families. In addition, the HSP70-Hom alleles of 31 patients with ankylosing spondylitis (AS) and 38 with reactive arthritis (ReA) were compared with each other and with 56 unrelated healthy HLA-B27 positive individuals. The results indicated that the HSP70-Hom polymorphic variation is not connected independently to the different pathogenesis of AS and ReA, as no statistically significant differences between the patient groups and/or controls could be found. The HSP70-Hom status was investigated also in 28 homozygous HLA typing cells and when compared with previously published results of HSP70-l and HSP70-2 polymorphisms, it appeared that these three MHC Class-III linked HSP70 genes segregated in fixed allelic combinations.