An HLA-B7 complementary DNA clone was used as a hybridization probe to analyze the segregation pattern of polymorphic class I restriction fragments in several families whose HLA types had been determined by serological techniques. In one family in which a crossover in the HLA region had occurred, a specific genomic fragment was mapped with respect to the crossover. In another family, a novel genomic fragment present in one child and absent in all other family members was observed. With the exception of this novel fragment, all polymorphic class I fragments observed in this study segregated with a serologically defined parental haplotype, a result consistent with HLA linkage.