The chromosomal location of the nu gene, which is responsible for hairlessness and athymus, was determined using six DNA markers (interleukin 3 [Il-3], Myhs, Acrb, Evi-2, Mpo, and Hox-2) on mouse chromosome 11. We constructed the high-resolution physical mapping of the six DNA markers on chromosome 11 by in situ hybridization using fluorescence-labeled cosmid probes. The results indicate the order of centromere-(41cM)-Il-3-(3cM)-Myhs- (4cM)-Acrb-(6cM)-Evi-2-(3cM)-Mpo-(5cM)- Hox-2. We have used congenic nude strains and examined which of the six DNA markers were derived from the original nude mouse. We found the Evi-2 locus is linked to the nu gene in all the informative, independent congenic nude strains. From these data, we could estimate the location of the nu gene, not only genetically but also physically within a region that spans approximately 17 megabases (9 cM) between the Acrb and Mpo genes.