Poly-arginine (e.g. (Arg)9) and arginine-rich peptides (e.g. TAT, penetratin), which belong to a class of peptides with cell-penetrating properties are neuroprotective. (Arg)9 provides significant neuroprotection in a dose–response manner following glutamic acid exposure (IC50=0.78 μM). Following kainic acid exposure, (Arg)9 is neuroprotective, but less effective than in the glutamic acid model (IC50=0.81 μM). (Arg)9 also shows neuroprotection following in vitro ischemia (IC50=6 μM).