Although ankylosing spondylitis (AS) is known to be strongly associated with the class I major histocompatibility complex antigen HLA-B27, B27 is probably not the only genetic factor involved in the pathogenesis of AS. Because of the involvement of tumor necrosis factor (TNF) in cartilage damage and the localization of the TNF genes in the proximity of the HLA-B locus, we investigated the association between AS and TNF alleles. The frequencies of the restriction fragment length polymorphisms linked to the TNF genes were determined in 73 AS patients and 81 controls. No differences were observed between AS patients and controls with respect to the frequencies of the TNF restriction fragment length polymorphisms.