Fibroblasts/myofibroblasts expansion is critical in the pathogenesis of pulmonary fibrosis. To date, most research has focused on profibrotic mediators, whereas studies on antifibrotic factors are scanty. In this study we explored the effect of acidic fibroblast growth factor (FGF-1) and FGF-1 plus heparin (FGF1+H) on fibroblast growth rate, apoptosis and myofibroblast differentiation. Heparin was used because participates in FGF-1 signaling. Growth rate was evaluated by WST-1 colorimetric assay, DNA synthesis by [³H]thymidine incorporation, and apoptosis by TUNEL and cleaved caspase-3. Expression of alpha-smooth muscle actin (SMA) was examined by immunocytochemistry, flow citometry, real-time PCR and immunoblotting. Despite of the induction of DNA synthesis, FGF-1+H significantly reduced fibroblasts growth rate. This correlated with a significant increase in apoptosis evaluated by TUNEL (41.6±1.4% versus 12.5±0.6% from controls; p<0.01), and cleaved caspase-3 (295±32 versus 200±19 ng/10⁶ cells from controls; p<0.05). Double immunostaining (SMA/TUNEL) revealed that the levels of induced apoptosis were similar in fibroblasts and myofibroblasts. FGF-1+H inhibited the effect of TGF-1 on myofibroblasts differentiation. By immunocytochemistry, -SMA positive cells were reduced from 44.5±6.5% to 10.9±1.9%, and by flow cytometry from 30.6±2.5% to 7.7±0.6% (p<0.01). Also, FGF-1+H significantly inhibited the TGF-1 induction of SMA quantified by real-time PCR and Western blot. This decrease was associated with a 35% reduction in TGF--induced collagen gel contraction. The effect of FGF-1+H was mediated by a significant decrease of TGF1-induced Smad2 phosphorylation. FGF-1 alone exhibited similar but lower effects. These findings suggest that FGF-1 can have an antifibrogenic role, inducing apoptosis of fibroblasts and inhibiting myofibroblast differentiation.