CHEMOTAXIS is an important component of wound healing, development, immunity and metastasis, yet the signalling pathways that mediate chemotaxis are poorly understood. Platelet-derived growth factor (PDGF) acts both as a mitogen and a chemoattractant1. Upon stimulation, the tyrosine kinase PDGF receptor-beta (PDGFR-beta) autophosphorylates2 and forms a complex that includes SH2(Src homology 2)-domain-containing proteins such as the phosphatidylinositol-specific phospholipase C-gamma (ref. 3), Ras-GTPase-activating protein (GAP)4, and phosphatidylinositol-3-OH kinase5. Specific tyrosine-to-phenylalanine substitutions in the PDGFR-beta can prevent binding of one SH2-domain-containing protein without affecting binding of other receptor-associated proteins6,7. Here we use phospholipase C-gamma (ref. 8) and PDGFR-beta mutants9-11 to map specific tyrosines involved in both positive and negative regulation of chemotaxis towards the PDGF-BB homodimer. Our results indicate that a delicate balance of migration-promoting (phospholipase C-gamma and phosphatidylinositol-3-OH kinase) and migration-suppressing (GAP) activities are recruited by the PDGFR-beta to drive chemotaxis towards PDGF-BB.