We have found a rare variant antigen (tentatively named B27KH) which reacts with B27-monospecific antisera, and some B40 group specific and Bw6- specific antisera. The sample with B27KH was submitted to the Japanese Red Cross Central Blood Center HLA Workshop 1994. The reaction pattern of B27KH was clearly distinguished from those of the B27 antigens encoded by B^* 27O2, 2704, 2705 and 2706. On the other hand, B27K11 and B^* 2707 antigen (originating from non-Japanese) showed very similar serological reaction patterns. Nevertheless, the B27KH allele was discriminated from B^* 2707 by PCR-SSOP typing, suggesting that the allele is a new member of the B27-group alleles.