AbstractMuscle growth and regeneration is controlled by locally produced growth factors which activate satellite cells and stimulate their proliferation, differentiation and fusion to form mature myotubes. Basic fibroblast growth factor (bFGF) has been previously shown to promote proliferation and inhibit differentiation of myoblastsin vitro.In comparison, thein vivorole of this growth factor is less well documented. In the present investigation on the role of bFGF in muscle regeneration, bFGF mRNA levels were studied in two experimental systems: (1) primary cell cultures derived from rat skeletal muscles, and (2) anin vivorat muscle injury model. bFGF mRNA was detected in myoblasts just prior to fusion and in myotubes of primary muscle cell cultures. In the non-injured muscle, bFGF mRNA transcripts were detected in myotubes but not satellite cells. In thein vivomuscle injury model bFGF mRNA was observed in myoblasts and in degenerating and regenerated myotubes. The significance of these experimental results in terms of the role played by bFGF in the myogenic programin vivoare discussed.