With the use of standard genetic techniques, we have mapped the T cell gamma-chain gene locus (Tcrg) to the proximal end of mouse chromosome 13. Close genetic linkage was demonstrated between a restriction fragment length polymorphism in the Tcrg locus and a locus (HlS) encoding a spermatocyte-specific histone electrophoretic variant (HlS) by using recombinant inbred strains. Because HlS is closely linked to the dominant visible marker extra toes (Xt), Tcrg must be within 5 cM of the beige (bg) locus. Mice homozygous for the recessive mutation beige (bg/bg) show diminished pigmentation, enlarged lysosomes in granulocytes, and a selective deficiency of natural killer cell function. The bg mutation in mice is an animal model for humans with Chediak-Higashi syndrome; we speculate that the human gamma-chain may be closely linked to the human mutation and may be a useful diagnostic tool. Seven restriction enzymes identify five haplotypes of the highly polymorphic gamma-chain in mice.