The observations were carried out in the adult normotensive rats of Wistar strain and in the genetically hypertensive rats developed by Koletsky, i.e., in the strain where is decreased turnover-rate of diencephalo-mesecephalic norepinephrine, increased CNS cholinergic activity accompanied by cholinergic supersensitivity and reduced stress-resistance. The effect of dihydroergotoxine was traced in holeboard and in the elevated plus-maze. Chronic dihydroergotoxine treatment shows "anxiolytic" effect in the elevated plus-maze (i.e., this drug alleviates aversion towards open space and height), increases directed exploration, elevates the rate of habituation of the locomotor-exploratory activity at all, and elevates the rate of habituation of directed exploration especially. The drug in the above mentioned parameters shows very expressive dependent effect, i.e., the effect being more or solely expressed in the genetically hypertensive rats of Koletsky type. The results of our recent series of experiments again suggest that is is well founded to use for the screening of the drugs with potential anxiolytic effect the genetically hypertensive rats of Koletsky type, i.e., the strain which by its CNS neurotransmitter abnormalities resembles deviations observed in the patients suffering from anxio-depressive disorders.