The human PDGFA gene, encoding the A chain of platelet-derived growth factor, has been previously cloned and characterized, but two conflicting chromosomal localizations have been presented. To resolve this controversy, we have now performed nonisotopic in situ hybridization using new genomic PDGFA subclones and analyzed somatic cell hybrid DNAs for the presence of human PDGFA by polymerase chain reaction. The results confirm our previous assignment of PDGFA to chromosome 7p22. New sequence data from the PDGFA locus have been obtained and analyzed. An unusual minisatellite, which includes an evolutionarily conserved protein-coding region of exon 4, was found within IVS4. The minisatellite includes an embedded polymorphic pentanucleotide microsatellite repeat. Analysis of this polymorphism and in situ hybridization both locate PDGFA outside the monosomic region in a patient with a de novo deletion of the short arm of chromosome 7 [del (7)(p22.1-pter)].