The effect of single and course administration of Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) in the dose 200 microg/kg on the rat hippocampus transcriptional profile were studied using cDNA microarray technology. It was shown that mRNA levels of 36 genes changed more than 2-fold after a single intranasal Selank administration, and 20 genes--after course administration. It should be noted that most of them encode proteins associated with the plasma membrane (including transmembrane proteins). This suggests that Selank is able to regulate ion homeostasis of hippocampal cells and thereby modulate different ion-dependent processes, which include the processes of learning and memory formation.