The analysis of HLA-DR5 haplotypes unravelled a new DRB3 polymorphism and permitted the identification of various associations between alleles of the DRB1 and DRB3 loci. This new polymorphism consists of a 10.5 kb Taq1 restriction fragment which was encountered in an African-American family (JS). In Caucasoids, the DRw11 allele has been previously observed only in association with the DRw52b allele. RFLP and oligonucleotide typing of HLA-DRw52 alleles associated with DRw11 showed, however, that 4 Caucasoid individuals from our panel carried the DRw52a allele and 1 the DRw52c allele. Similarly, DRw12, which is usually associated with DRw52b, was encountered with DRw52a in 1 Chinese and with DRw52c in an African-American and a Chinese panel member. The study of DRB3 alleles associated with DRw11 and DRw12 indicates that, similar to serology, RFLP studies become particularly informative when individuals of different races and ethnic origins are studied.