HLA DQ beta chain, in particular amino acid at position 57, has been reported to contribute to susceptibility and resistance to Type 1 (insulin-dependent) diabetes mellitus in Caucasians. Resistance has been proposed to be conferred by aspartic acid at this position. To ascertain the association of HLA DQ beta and DR beta genes with Type 1 diabetes in Japanese subjects, ten Japanese Type 1 diabetic patients were investigated at DNA level. Genomic DNA was amplified by polymerase chain reaction, and dot blot analysis was carried out using the amplified DNA with allele specific oligonucleotide probes. All patients had aspartic acid at position 57 of at least one of their two DQ beta chains, and there was no significant difference of amino acids at the same position of DR beta chain in patients compared to control subjects. These data indicate that the protective role of aspartic acid at position 57 of DQ beta chain is less significant in Japanese compared with Caucasian subjects.