The expression of platelet-derived growth factor (PDGF) is controlled in a very complicated manner. To clarify the mechanism of regulation of the PDGF-A chain gene, deletion analysis of the 5'-flanking region was performed. We identified a positive regulatory element 25 base pairs (bp) upstream of TATAA, a negative element 135 bp upstream, a positive element 223 bp upstream and a negative element further upstream. These regulatory sites of the PDGF-A chain gene may be involved in tissue specificity, developmental regulation, and transformation. In addition, our analysis suggested the presence of a strand non-specific single-stranded DNA binding nuclear protein in the positive regulatory element 25 bp upstream of TATAA.