We previously reported that dipyridamole decreased platelet-derived growth factor (PDGF) levels in human serum by lowering the release of PDGF during blood clotting. In this study, we have shown that this effect is specific for dipyridamole, and is not shown in other anti-platelet drugs such as aspirin, trapidil or ticlopidine. In addition, dipyridamole has been shown to decrease the PDGF level selectively, but not the levels of other factors from alpha-granules in platelets (beta-thromboglobulin and platelet factor IV). These data indicate that dipyridamole may be an effective drug for preventing PDGF-related disorders.