A family with known accumulation of ankylosing spondylitis (AS) was examined clinically, radiologically and by HLA tissue typing. Among 17 individuals of three generations there were four carriers of classical AS, all HLA-B27-positive. Five carriers of HLA-B27 were clinically and radiologically healthy, but three of them were below the age of 30, thus still being at risk of developing AS. The numerical relation between first degree relatives with and without HLA-B27 was 10:7. Genotype reconstruction of the great grandparents lead to the conclusion, that they were carriers of two different haplotype combinations, HLA-1/HLA-B27 and HLA-2/HLA-B27. Both haplotype combinations proved to be associated with AS. Among the offsprings of these great grandparents the combination of HLA-2 with HLA-B27 occurred in 3 of the 4 ankylosing spondylitics and in four of the six healthy HLA-B27-carriers. The question whether a haplotype combination of HLA-2 and HLA-B27 leads to an increased risk for AS cannot be decided without further systematic genotype determinations.