Animals and intravenous injections. Four and a half month old to 5½-month-old mdx mice were used in these experiments (n = 3). The experiments were carried out in the Biomedical Sciences Unit, University of Oxford according to procedures authorized by the UK Home Office. Pip6-PMO conjugates were prepared in 0.9% saline solution at a final dose of 12.5 mg/kg. The 160 µl total volume was administered via the tail vein of anaesthetized mice. Two weeks later mice were sacrificed by CO 2 inhalation, and muscles and other tissues harvested and snap-frozen in cooled isopentane before storage at -80 °C.