The heptapeptide Semax, an analogue of the N-terminal adrenocorticotropic hormone fragment (4-10) (ACTH(4-10)), has been shown to exert a number of neuroprotective effects. There are some investigations that connected these effects with the increase of neurotrophin gene expression under the peptide drug application in neuron cell cultures [M.I. Shadrina, O.V. Dolotov, I.A. Grivennikov, P.A. Slominsky, L.A. Andreeva, L.S. Inozemtseva, S.A. Limborska, N.F. Myasoedov, Rapid induction of neurotrophin mRNAs in rat glial cell cultures by Semax, an adrenocorticotropic hormone analogue, Neurosci. Lett. 308 (2001) (2) 115-118]. In this work, we examined the action of Semax on rapid changes of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) gene expression in vivo. Male Wistar rats were treated for 1h with Semax (50 microg/kg, single intranasal application) and neurotrophin gene expression in rat brain was analyzed by real-time polymerase chain reaction (PCR). It was revealed that an intranasal application of Semax increased the expression of both neurotrophin genes in rat hippocampus. Bdnf gene expression also increased in the brainstem and cerebellum. Ngf gene expression decreased in rat frontal cortex. Thus, Semax induces rapid, gene- and region-specific changes in neurotrophin gene expression in normal rat brain.