Studies of several brain diseases have demonstrated that peripherally administered EPO crosses the BBB and alters neuronal survival and functional recovery.8, 56 One possible explanation of the functional gap between MK-X and EPO could be that a small peptide has potential advantages in crossing the BBB.57 If so, because acute brain ischemia is strongly time-dependent, the protective effect of MK-X may be stronger than that of EPO under our experimental conditions. This evidence concerns the gene EPO and brain ischemia.