The technique of SSCP was applied to the molecular subtyping of the HLA-DR4 group of alleles. SSCPs were defined in 16 cell line DNAs, representing the alleles DRB1*0401-*0411 (except DRB1*0409), using group-specific PCR amplification, nondenaturing polyacrylamide gel electrophoresis, and silver staining. Three sets of gel electrophoresis conditions were necessary to differentiate the 10 alleles tested. The SSCPs defined in the cell line DNAs were validated by analysis of 145 unrelated HLA-DR4-positive individuals previously genotyped for DRB1*04 alleles by sequence-specific oligotyping. This study demonstrates the suitability of the SSCP technique for defining DRB1*04 alleles, particularly when a small number of samples require typing.