We previously reported a simple technique for HLA-DQB genotyping by digestion of polymerase chain reaction-amplified genes with restriction endonucleases (PCR-RFLP method). However, this method has some problems in that some heterozygotes cannot be discriminated from each other. Furthermore, concomitantly amplified product derived from the DQB2 gene by the primers used previously also obstructs precise DQB1 genotyping. To resolve these problems, we have developed two different pairs of specific primers for selective amplification of the DQB1 gene and also used restriction endonucleases which have either a single cleavage site or, alternatively, no cleavage site in the amplified DNA region, depending on the HLA-DQB1 alleles, making reading of RFLP band patterns much easier. The second exon of the DQB1 gene was selectively amplified by DQw1 group-specific primers and/or DQw2,3,4 group-specific primers using genomic DNAs from 70 HLA-homozygous B-cell lines and 50 healthy Japanese. Of the seven DQw1-associated DQB1 alleles, six alleles could be defined by digestion of 6 restriction enzymes, although DQB1*0602 and DQB1*0603 could not be discriminated from each other because of unavailability of suitable enzymes. Similarly, all of the six DQw2,3,4-associated DQB1 alleles could be defined by digestion of 5 restriction enzymes. Using this modified PCR-RFLP method, complete DQB1 genotyping of all heterozygotes is possible except for discrimination between DQB1*0602 and 0603. Thus this method is simpler and more practical for a routine DNA typing than the PCR-SSO method or our previous PCR-RFLP method.