PDGF is a mitogenic protein stored in platelets and released upon platelet degranulation. Recent evidence indicates that PDGF plays an important role in both physiologic and pathophysiologic processes, particularly in tumorigenesis, wound healing, pulmonary fibrosis, and atherogenesis. In addition to its mitogenic potential, it has been reported that PDGF stimulates monocyte chemotaxis. Since the recruitment of monocytes from the peripheral vasculature is an important event in vivo, the potential role of PDGF as a monocyte chemoattractant has significant biologic implications. However, we now report that homogeneous human PDGF from platelets and a recombinant PDGF-2 homodimer do not stimulate monocyte chemotaxis. In contrast to previous reports these results indicate that PDGF is not a monocyte chemoattractant.