The study was undertaken to determine the effects of HLA-B27 subtypes on susceptibility to ankylosing spondylitis (AS) in Taiwan Chinese, a polymerase chain reaction-restrictive fragment length polymorphism (PCR-RFLP) method was developed for subtyping of HLA-B27. In this series, there are 62 patients with AS who were tested HLA-B27 positive serologically and 738 normal persons over the age of 65. Among the 738 normal controls, 42 (5.7%) were HLA-B27 positive. There were six (14.3%) homozygous for B2704, 18 (42.9%) heterozygous for B2704, 2 (4.8%) double heterozygous for B2704 and B2705, one (2.3%) double heterozygous for B2704 and B2706, 2 (4.8%) homozygous for B2705, 11 (26.1%) heterozygous for B2705, and 2 (4.8%) heterozygous for B2706. In our patients with AS, 37 (59.7%) were homozygous for B2704 and 25 (40.3%) were heterozygous for B2704. The HLA-B27 carrier rate in Taiwan healthy old persons is estimated at 5.7%. Susceptibility to AS is determined by homozygosity for B2704. However, B2705 may be an indicator of protection against AS in Taiwan Chinese.