Cell-mediated gene therapy requires an in vitro amplification of modified cells prior to their injection into target tissue. Since the proliferative capacity of normal human cells is limited, we have tested a method to follow in vitro the proliferative potential of human satellite cells. Our results show that telomere length can be used to predict the proliferative potential of human satellite cells. In this short communication, the telomere shortening and the limited replicative potential are discussed in the context of the possible use of human satellite cells for gene transfer and why cell-mediated gene therapy has been less successful in humans than in mice.