Although individual TCRVBV gene segments exhibit limited polymorphism, human T-cell receptor beta (TCRB) haplotypes are characterized by multiple different combinations of allelic markers. This observation suggests that genetic recombination may have played a role in the generation of these haplotypes. Meiotic recombination in a region spanning -250 kilobases (kb) at the 3' end of the TCRB gene complex was investigated by extended family studies and by analysis of single sperm. Segregation patterns of polymorphic TCRB markers in families allowed the assignment of TCRB alleles to parental haplotypes and detection of recombinants among the offspring. Among the 178 informative paternal meioses, four (-2%) were recombinant, whereas no recombinants were found in the 199 maternal meioses. In addition, segregation of two allelic markers was examined in a total of 1101 individual sperm from two heterozygous donors to detect exchange events in this region. The results revealed a similar rate of recombination, -1.3%, which, along with the family data, suggests that at, least in males, meiotic recombination in this 250 kb region may be six times higher than the "average" rate of 1% per 106 bases that has been estimated for the human genome.