Macrophage colony-stimulating factor (CSF-I) is a key regulatory cytokine for amelogenesis, and ameloblasts synthesize CSF-I. We hypothesized that PDGF stimulates DNA synthesis and regulates CSF-I in these cells. We determined the effect of PDGF on CSF-I expression using MEOE-3M ameloblasts as a model. By RT-PCR, MEOE-3M expressed PDGFRs and PDGF A- and B-chain mRNAs. PDGF-BB increased DNA synthesis and up-regulated CSF-I mRNA and protein in MEOE-3M. Cells transfected with CSF1 promoter deletion constructs were analyzed. A PDGF-responsive region between - 1.7 and - 0.795 kb, containing a consensus Pea3 binding motif, was identified. Electrophoretic mobility shift assay (EMSA) showed that PDGF-BB stimulated protein binding to this motif that was inhibited in the presence of anti-Pea3 antibody. Analysis of these data provides the first evidence that PDGFBB is a mitogen for MEOE-3M and increases CSF-I protein levels, predominantly by transcription. Elucidation of the cellular pathways that control CSF-1 expression may provide novel strategies for the regulation of enamel matrix formation.