Human adenovirus (AV) is a favored vector for delivery of therapeutic genes into certain target cells, such as skeletal muscle cells for gene therapy. Here we show that replication-defective (E1 + E3 deleted) human type 5 adenovirus (AV) recombinants containing a reporter gene insert (RSV-luciferase or RSV-Lux) can very efficiently transduce cultured human myoblasts. However, transduction efficiency is about one order of magnitude less in cultured myotubes 16 days postfusion. The high transduction of myoblasts by AV-RSV-Lux could be effectively blocked by an arginine-glycine-asparagine (RGD) oligopeptide that serves as a ligand for the natural internalization receptor of AV. The normalized level of beta 3/beta 5-integrin, the main component of the internalization receptor for AV is about three times as abundant in myoblasts than in myotubes. This could contribute, among other things, to the relatively high susceptibility of myoblasts to AV infection and AV-mediated gene transduction.