The met oncogene is the normal counterpart of a chemically-induced transforming gene. The chromosomal localization of met is 7q21-31. In a patient with myelofibrosis and an interstitial deletion on 7q, we demonstrate that a Taq I polymorphism for the met oncogene is lost in the neoplastic cells, thus indicating that the deletion occuring in the long arm of chromosome 7 involves the met locus.