Polymorphism in the germline repertoire of T-cell receptor (TCR) variable α and β (Vα and Vβ) genes could alter the relative abilities of individuals in a population to respond to particular antigens. Variation in the number of germline Vα and Vβ gene segments has been reported in wild mice and in different inbred mouse strains. A previous study of the human Vβ gene germline repertoire failed to reveal a similar degree of polymorphism in the numbers of Vβ gene segments. We have now carried out a survey of 10 different Vα gene segment subfamilies containing approximately 23 Vα gene segments in a panel of 120 unrelated individuals by hybridization and failed to find any evidence for Vα repertoire polymorphism. To determine if significant germline polymorphism does occur in humans at the level of individual V gene segments, we determined the nucleotide sequences of eight copies of the Vα21 gene segment derived from seven unrelated individuals. Polymorphic differences between these sequences defined three different alleles. One of these alleles contains a frameshift mutation which would cause premature termination of the protein product. The presence of this null allele among the eight sequences determined suggests that functionally relevant germline polymorphism of human TCR V gene segments may occur by mechanisms other than gene duplication or deletion.