An HLA-DR typing system that uses sequence-specific oligonucleotide (SSO) probes conjugated to horseradish peroxidase (HRP) for analyzing DRB alleles amplified by the polymerase chain reaction has been developed. Using 25 HRP-SSO probes and two primer pairs for generic and for DRB1 locus-specific amplification, we can distinguish 31 of 34 HLA-DRB1 alleles. This procedure is suitable for typing heterozygous samples from a variety of sources, including cDNA templates, and can detect in a simple and rapid dot-blot format allelic variants not distinguishable by serological methods. It should prove valuable for tissue typing, determining individual identity, and studies of disease susceptibility.