The gene controlling the expression of the murine Gte idiotype marker was mapped within the Igh-V gene complex. This idiotypic marker was identified in B6, C.B-20 and A/J and C.AL-20 anti-GAT antisera, but either was not detectable or was present in very low quantities in the anti-GAT antisera obtained from BALB/c, BAB-14, SM/J, NZW, and NZB mice. The data are consistent with the interpretation that the latter 5 strains do not process Igh-Gte genes and the Igh haplotypes of these strains represent examples of crossing over within the Igh complex. Furthermore, the expression of the Gte idiotype(s) is not influenced by the Lyt-3 linked genes that control the kappa light chain polymorphism. Segregation analysis with 52 recombinant inbred strains confirmed the close linkage of Igh-Gte idiotype with Igh-1b locus. The recombination frequency between these loci was calculated to be 1 +/- 0.7 percent. Furthermore, by using B X D recombinant inbred strains, the Igh-Gte gene was mapped within the Igh-V region gene closely linked to the Igh-Np, Igh-Nbp, and Igh-BgI genes.