Platelet-derived growth factor BB (PDGF BB) and the PDGF receptor b are expressed on mesotheliomacells, but their biological function has not yet been defined. In the present study we used Boyden chambersfitted with filters coated with the adhesive matrix proteins fibronectin, laminin, collagen type IV or the non-matrixadhesive molecule poly-L-lysine (PLL). Mesothelioma cells migrated towards PDGF BB at concen-trationsranging from 0.78 to 12.5 ng/ml if matrix proteins were present as adhesive substrates. This migrationwas integrin dependent since the same cells failed to migrate if the adhesive interactions necessary for migra-tionwere provided by molecules other than integrins. Migration of mesothelioma cells on fibronectin, lamininor collagen-type IV in response to PDGF BB was inhibited if the cells were pretreated with blocking anti-bodiesto a3b1 integrin. These findings describe for the first time PDGF BB as a chemoattractant for malig-nantmesothelioma cells and that collaboration between PDGF receptor b and integrin a3b1 is necessaryfor the motile response of these cells to PDGF BB.©Kluwer Academic Publishers