We utilized the technique of restriction fragment length polymorphism (RFLP) analysis in order to examine class I major, histocompatibility complex genes in 52 Alabama ankylosing spondylitis patients and 107 local control subjects. A 9.2-kilobase PvuII RFLP was identified using the class I-specific B7 cDNA probe pDP001 that was closely associated with ankylosing spondylitis, most specifically with peripheral joint (including shoulder and hip) involvement. This fragment is associated with human leukocyte antigen A3 and A9 alleles, and segregation analysis in 11 multiplex families showed the RFLP to frequently segregate independently of B27 haplotypes. Two more recent studies have not confirmed the association of the 9.2-kilobase PvuII RFLP with ankylosing spondylitis per se, believed to be due to clinical and possibly genetic differences between the patient groups studied. These data strongly suggest at least one other major histocompatibility complex class I gene to be operative in predisposition to or modification of ankylosing spondylitis. © 1988.