We have isolated a new marker (cos11-5TH) that detects an MspI restriction fragment length polymorphism in the 5' region of the human tyrosine hydroxylase gene (TH) on chromosome band 11p15.5. This region of human chromosome 11 contains several important loci for disease phenotypes including Beckwith-Wiedemann syndrome (BWS), Wilms' tumor, and embryonal rhabdomyosarcoma. Thus, identification of new polymorphic markers in this region are important for future gene mapping and linkage analyses. To better define the region of 11p15.5 deleted in embryonal rhabdomyosarcoma, this new marker was used to investigate allelic losses in embryonal rhabdomyosarcoma tumors.