The 5' untranslated region of HLA-F contains a polypurine tract comprising repeats of tri- and hexa-nucleotide motifs. We have recently demonstrated that this polypurine tract is highly polymorphic by using the polymerase chain reaction. Here, we demonstrate that some of the alleles can be explained by a deletion of approximately 100 bp DNA and show that alleles of this novel, highly polymorphic locus are as strongly associated with haemochromatosis as HLA-A3 or D6S105-8. The observed frequency of heterozygosity at HLA-RF is extremely high (95%) and this locus has been found to be informative in pedigrees that are non-informative at HLA-A and D6S105. We also show an example of replication slippage at HLA-F in one pedigree.