Abstract:The HLA‐B70 antigen is among the most common antigens present in African Americans; however, monospecific serologic reagents defining B70 and its subtypes, B71 and B72, are rare. We have recently reported the molecular characterization of a B71 allele (B*1510) from an African American individual carrying the haplotype HLA‐A30, Cw3, B71(w6). In order to better define the degree of polymorphism of molecules carrying the B71 serological specificity in the human population, we have used serology, cDNA sequencing, and PCR/SSOP typing to characterize B71 alleles from additional individuals from different ethnic populations and carrying different class I haplotypes. All carried either B*1510 or B*1518 alleles. Other HLA‐B alleles isolated from these individuals (B*5001, B*4901, B*3501, B*3701) were identical to previously reported sequences except for a novel B41 allele (B*4102) identified in one Hispanic individual. This allele has concurrently been identified by Rufer and colleagues in Caucasian individuals. The B*4102 allele differs from B*4101 at codons 95 (Leu/Trp) and 97 (Ser/Arg). In addition, the B*4102 allele differs from B*4101 by two silent substitutions at codons 94 (ACC/ACT) and 99 (TAC/TAT). Since the polymorphic sequence present in B*4102 is also present in other HLA‐B alleles (e.g., B*2707, B*4002, B*0702), it may represent a gene conversion cassette. The allelic diversity at the class I loci and the scarcity of monospecific alloantisera support the importance of the application of molecular based methods to identify HLA class I alleles in matching unrelated donor/recipient pairs for bone marrow transpla