The HLA Class I sequences included in this compilation are taken from publications listed in the papers: Nomenclature for factors of the HLA system, 1991 (1), Nomenclature for factors of the HLA system, 1990 (2) and factors of the HLA system, 1989 (3). Due to the increased number of sequences we have only included sequences for exons 2, 3 and 4 in this compilation. Where discrepancies have arisen between reported sequences, the original authors have been contacted where possible, and necessary amendments to published sequences have been incorporated into this alignment. Future sequencing may identify errors in this list and we would welcome any evidence that helps to maintain the accuracy of this compilation. In the sequence alignments, identity between nucleotides is indicated by a hyphen (-). An unavailable sequence is indicated by a period (.). Gaps in the sequence are inserted to maintain the alignment between different alleles showing variation in amino acid number. A number of sequences that do not appear in the last Nomenclature report are given in the sequence alignment. The HLA allele and the submitting authors are the following; -BeWo C.1 (S. Ellis); Cl.10, Cl.9 (L. Cianetti), Cw6W (E. Weiss); A*68012, B*5104, Cw*0803 (P. Parham); B*4802, B*52012, B*3903, C*X (D. Watkins); B*39013 (M. Takiguchi). Full information regarding these sequences will be given in the next Nomenclature report. In addition, the B*2705W allele shown in this sequence alignment and reported by the group of E. Weiss was found to differ by 3 silent substitutions from the B*2705 (that appeared in the last published alignment). Differences are the following: B*2705: position 245 (Exon 3) 'T'; position 71 (Exon 4) 'A'; position 161 (Exon 4) 'G'. B*2705W: position 245 (Exon 3) 'G'; position 71 (Exon 4) 'G'; position 161 (Exon 4) 'A'.