A porcine comparative map based on 83 coding loci was constructed. Comparisons to the human and mouse genetic maps revealed linkage conservation between humans and pigs more extensive than that between any of these and the mouse. The average lengths of conserved chromosome segments between pig and human and between pig and mouse were estimated at 37 and 21 cM, respectively. Rearrangements of gene orders within homologous chromosome segments were found to be common among these distantly related mammals. The development of a comparative map is an advance in pig genome analysis and contributes to the dissection of mammalian genome evolution.