Bulk populations of T-cell receptor (Tcr) γδ-expressing splenocytes from different inbred strains of mice were examined for the diversity of Tcr γδ proteins. Immunoprecipitations with anti-Cγ1/2, anti-Cγ4, and anti-Vγ1 sera demonstrated that splenocytes from B10.BR, C57BL/6, and C57L strains of mice expressed the same array of Tcrγ proteins, namely Vγ1-Cγ2, Vγ1-Cγ4, and Vγ2-Cγ1, although the Tcr γδ heterodimers observed for each of these strains were biochemically distinct. Examination of bulk splenic Tcr γδ heterodimers from several other inbred strains of mice demonstrated that each of the strains could be categorized into one of three basic phenotypes. For several reasons, the differences observed between the strains appeared to be solely dependent on polymorphisms of the Tcrg loci. First, F1 mice co-expressed both parental Tcr γδ phenotypes. Second, the distinguishing polymorphism between mice of phenotype 1 and phenotypes 2 or 3 was due to the presence of an N-linked glycosylation site within the Tcrg-C1 gene segment, previously described for BALB.B and C57BL/6 Tcrg-C1 genes. Finally, the Vγ1-Cγ4 polymorphism between mice of phenotype 3 and phenotypes 1 or 2 was due to differences in core protein size. Furthermore, the three defined Tcrγ chains were expressed independently of the major histocompatibility complex (MHC) haplotype. Although no striking qualitative differences in Tcr γδ heterodimers were observed between strains (including those with autoimmune disorders), a quantitative difference in the relative amount of Cγ4-encoded proteins was observed on Tcr γδ splenocytes from both newborn euthymic and adult athymic mice when compared to adult Tcr γδ splenocytes from euthymic mice. These results demonstrate that genetic polymorphisms exist among different mouse strains and suggest that selective developmental pressures may govern Tcr γδ expression. © 1990 Springer-Verlag.