The mouse mutation hairy ears (Eh) originated in a neutron irradiation experiment at Oak Ridge National Laboratory. Subsequent linkage studies with Eh and other loci on Chr 15 suggested that it is associated with a chromosomal rearrangement that inhibits recombination since it shows tight linkage with several loci occupying the region extending from congenital goiter (cog) distal to caracul (ca). We report here (1) linkage experiments confirming this effect on recombination and (2) meiotic and mitotic cytological studies that confirm the presence of a chromosomal rearrangement. The data are consistent with the hypothesis of a paracentric inversion in the distal half of Chr 15. The effect of the inversion extends over a minimum of 30 cM, taking into account the genetic data and the cytologically determined chromosomal involvement extending to the region of the telomere.