The bipotential glial progenitor cells (O‐2A progenitors), which during development of the rat optic nerve give rise to oligodendrocytes and type 2 astrocytes, are stimulated to divide in culture by platelet‐derived growth factor (PDGF), and there is evidence that PDGF is important for development of the O‐2A cell lineage in vivo. We have visualized PDGF mRNA in the rat optic nerve by in situ hybridization, and its spatial distribution is compatible with the idea that type 1 astrocytes are the major source of PDGF in the nerve. We can detect mRNA encoding the A chain, but not the B chain of PDGF in the brain and optic nerve, suggesting that the major form of PDGF in the central nervous system is a homodimer of A chains (PDGF‐AA). PDGF‐AA is a more potent mitogen for O‐2A progenitor cells than is PDGF‐BB, while the reverse is true for human or rat fibroblasts. Fibroblasts display two types of PDGF receptors, type A receptors which bind to all three dimeric isoforms of PDGF, and type B receptors which bind PDGF‐BB and PDGF‐AB, but have low affinity for PDGF‐AA. Our results suggest that O‐2A progenitor cells possess predominantly type A receptors, and proliferate during development in response to PDGF‐AA secreted by type 1 astrocytes.