Myogenesis is thought to be regulated by the MyoD family of regulatory genes, which includes MyoD, myogenin, MRF-4/myf-6, and myf-5. In situ hybridization studies of vertebrate skeletal muscle development have shown the colocalization of the MyoD family of regulatory genes to specific stages of muscle development. Although many studies have analyzed the regulatory role of these genes during myogenesis, there have been few reports dealing with the activation of these myogenic regulatory genes by exogenous agents. We have previously shown that muscle morphogenetic protein induces myogenesis in clonal populations of avian pluripotent stem cells. The current study was designed to examine the ability of muscle morphogenetic protein to induce myogenesis in a clonal population derived from the established fibroblastic Swiss-3T3 cell line. Swiss-3T3 cells were cloned to generate separate cell populations, tested for pluripotency, propagated through 690 cell doublings, retested for pluripotency, treated with muscle morphogenetic protein, and examined for the induction of gene expression using probes for the transcription products of MyoD and myogenin. Muscle morphogenetic protein induced the expression of mRNAs for MyoD and myogenin, suggesting a role for this compound as an exogenous activator of myogenesis.