MDK and PTN are two members of a family of heparin-binding cytokines thought to be involved in a number of developmental processes. The locations for these genes were determined in man and mouse using somatic cell hybrid analysis and interspecific backcross analysis. Human MDK was mapped to 11p13-->p11. MDK in the mouse (Mdk) was mapped to a syntenic region of mouse Chromosome 2. A pseudogene of Mdk was mapped to mouse Chromosome 11. The closely related human gene PTN was mapped to a separate location on human chromosome region 7q22-->qter.