We describe a rapid method of HLA class I typing using the polymerase chain reaction and oligonucleotide hybridisation that eliminates the requirements for viable lymphocytes and allows subtypes to be defined. We have used this to demonstrate that the predominant subtype of HLA-B27 in the Gambia, West Africa, is HLA-B*2703, which is very rare or absent in other racial groups. This subtype differs from the common Caucasian HLA-B27 subtypes in its recognition by cytotoxic T cells. We propose that HLA*B-2703, unlike other HLA-B27 subtypes, may not be associated with ankylosing spondylitis, thus accounting in part for the rarity of this condition in black populations.