It remains unknown which factor(s) control mast cell recruitment in chronic immune reactions. Although TGF-beta has been shown to function as a potent chemotactic factor for monocytes, fibroblasts, and neutrophils, its effect on mast cells has not been previously determined. In this study, TGF-beta 1 was shown to cause directed migration of cultured mouse mast cells at femtomolar concentrations, with a maximal chemotactic response observed at 25 fM. Moreover, chemotaxis to TGF-beta was also seen using freshly isolated rat peritoneal mast cells. Addition of neutralizing Ab to TGF-beta abrogated its chemotactic activity for both freshly isolated rat peritoneal mast cells and cultured mouse mast cells, whereas an irrelevant species-matched control Ab had no effect. Checkerboard analysis confirmed the mast cell chemotactic activity after exposure to concentration gradients of TGF-beta. Mast cells were observed to undergo rapid and extensive shape changes on exposure to TGF-beta, assuming a polarized morphology in preparation for migration. Other known mast cell chemoattractants including laminin, c-kit ligand, and IL-3 were found to be considerably less potent on a molar basis in inducing directed migration. Affinity cross-linking studies identified TGF-beta binding proteins with M(r) at 70 and 288 kDa, consistent with types I and III TGF-beta receptors on the mast cells. In summary, TGF-beta is the most potent chemoattractant described for mast cells and conceivably relevant, because pathologic processes mediated by TGF-beta are often associated with mast cell accumulation.