Creatine transporter 1 (CT1) defect is an X-linked disease that causes severe neurological impairment. No treatment has been available for this condition so far. Because the transport of creatine (Cr) precursors Gly and Arg is not affected in this disorder, we tested the possible corrective effect of these two amino acids on Cr depletion in lymphoblasts lacking the transporter. Substrates enriched with Arg or Arg plus Gly increased the concentration of intracellular Cr in affected cells as well as in control cells. The greatest effect was obtained with 10 and 15 mM Arg and 10mM Arg plus Gly. These results encourage an in vivo trial with Cr precursors in CT1 defect.