The segregation of Mlsa with respect to genes localized distally on mouse chromosome 1 was examined in two sets of recombinant inbred (RI) strains. In order to localize Mlsa, a linkage map based on analysis of both interspecific backcross mice and multiple sets of RI strains was utilized: (centromere) - Ren-1,2 - 10 centimorgans (cM) - At-3 - 8cM-Apo-A2/Ly-17 - 2cM - Spna-1 - 4cM - Akp-1 - (telomere). The Mlsa allele was mapped to a region that extended just centromeric of Ly-17 (one crossover in 40 RI strains) to just telomeric of Spna-1 (no crossover in 40 RI strains). The identification of multiple polymorphic loci in the region of Mlsa should allow precise gene localization and assist in efforts to clone this gene.