The effect of taftcine (Thr-Lys-Pro-Arg) and its analog TP-7 (Thr-Lys-Pro-Arg-Pro-Gly-Pro) on rat behavior and serotonin brain exchange was studied in 95 adult male Wistar rats neonatally administered with 5,7-dihydroxytriptamine. Intracutaneous administration of both peptides (300 micrograms/kg) was found to result in weakening perception of stress situations; an increase in stability of investigation behavior and normalization of serotonin level in the brain of rats with chronic deprivation of serotoninergic system activity. Anxiolytic and psychostimulant activities of TP-7 are more pronounced than those of tafcine.