The effect of the new regulatory peptide Semax (ACTH4–10 fragment) on the electroencephalogram of a healthy person was studied. Semax was administered at 0.5 mg/kg intranasally in 9 volunteers without causing any nervous system pathology. The control group comprised 6 examinees treated in the same way with distilled water. The effect of Semax manifested itself on the electroencephalogram as a boost of biopotential strength in all ranges but especially in that of the α-rhythm, the zonal differences of which were enhanced, without any pathological signs being evident.