Normal myoblasts have a strictly limited growth potential and senesce after a defined number of population doubling. The objective of this study was to determine whether the proliferative capacity of human myoblasts could be extended without inhibiting myogenic differentiation. We have established a stable transfected human myoblast cell line that expresses the SV 40 large T antigen under the control of the human vimentin promoter. We show that these cells have an increased proliferative capacity compared with that of normal myoblasts. Indeed, the final proliferative capacity was increased to 19 passages (5 for normal myoblasts). Moreover, they retained their capacity to differentiate fully, as indicated by their morphology and electrophysiological properties as well as by the expression of different markers of differentiation. The generation of human myogenic cell lines with the ability to proliferate for a longer period of time than primary myoblasts and while retaining the capacity to differentiate into myotubes could provide a valuable tool for the derivation of cell lines from human diseased muscle cells.