The finding that PDGF production is common in normal as well as transformed cells indicate that PDGF has a function in autocrine and paracrine stimulation of cells in several physiological and pathological conditions. The expression of mRNA for the two chains of PDGF are independently regulated. The fact that the different dimeric forms of PDGF have different functional effects, indicate that the cellular response to PDGF may be more complex than previously thought, and may involve binding to more than one receptor. The cellular effects ascribed to PDGF, growth stimulation, ruffling and chemotaxis, seems to be mainly associated with B chain containing dimers. The function of PDGF-AA remains to be elucidated.