In this report we assigned to chromosome 10q the human oncogene PTC frequently associated with the papillary type of thyroid carcinoma. Using an informative panel of human-mouse somatic cell hybrids and 'in situ' hybridization to human metaphase chromosomes, we localized the PTC gene at bands q11-q12 of chromosome 10. These bands belong to one of the two regions on chromosome 10 linked to the cancer syndrome multiple endocrine neoplasia type 2A (MEN2A). Therefore, it is suggested that genes clustered in certain regions of chromosome 10 could be involved in the developmental regulation of the thyroid gland.