Previous studies have shown that cultured Schwann cells secrete platelet-derived growth factor (PDGF) and express PDGF receptors which transmit a mitogenic response particularly when their levels are upregulated by elevation of intracellular cAMP. In this study the expression of PDGF and PDGF alpha- and beta-receptors in the peripheral nervous system (PNS) has been examined by studying dorsal root ganglia and sciatic nerve. Using the monoclonal anti-PDGF antibody, PGF-007, relatively high levels of PDGF were detected in cells of the neonatal rat dorsal root ganglia and sciatic nerve. The location and morphology of these cells indicated that they were Schwann cells while neurons of the dorsal root ganglia were less strongly labeled. The levels in Schwann cells declined during the first postnatal weeks. In the adult rat, low levels of PDGF were detected on myelinated nerve fibers while unmyelinated fibers continued to express higher levels of PDGF. Antisera specific for the PDGF alpha- and beta-receptor revealed high levels of both receptors in the neonatal rat PNS. In the adult rat peripheral nerve both receptors were detectable in unmyelinated nerve fibers. The PDGF beta-receptor, but not the alpha-receptor, was detected at low levels on myelinated nerve fibers. Teased nerve preparations, as well as freshly dissociated sciatic nerve cells, were used to substantiate the findings in frozen tissue sections. Neurons of the dorsal root ganglion expressed PDGF and PDGF alpha- and beta-receptors in all the stages of postnatal development examined. These results indicate that PDGF might play a role in the development of the PNS and in maintenance of peripheral neurons.