Acute susceptibility of the mouse to Leishmania donovani is largely determined by a single locus designated Lsh. Linkage between the Lsh locus and the Chromosome 1 marker Id-1 was detected using several sets of recombinant inbred strains. Chromosome 1 linkage was confirmed in backcross generations using isoenzymes and a cytogenetic marker. The data indicate that the gene order is centromere-Lsh-Id-1-ln-Dip-1. The estimated recombination frequency between Lsh and Id-1 is 0.12 +/- 0.04. This mapping is away from the known histocompatibility loci.