Some biochemical patterns of the neurotransmitter system activity were studied in mitochondrial fraction of rat brain locomotor cortex and caudate nucleus under normal conditions as well as after short-term (60 min) and long-term (3 weeks) administration of amphetamine at a dose of 2.5 mg/kg. Under these conditions some alterations were detected in activity of monoamine oxidases of the A and B types involved in utilization of neurotransmitters as well as in content of catecholamines (dopamine, noradrenaline and serotonin). Similar alterations were also observed in the ratio between content of biogenic amines and their metabolic end-products: homovanillic and 5-hydroxyindole acetic acids which indicates the rate of the neurotransmitter metabolism. These alterations in parameters of the neurotransmitter systems were strongly individual and dissimilar depending both on localization in brain structures and on the step of the pharmacological treatment. Amphetamine appears to cause definite reciprocal alterations of the patterns studied: activation of the catecholamine-dependent mediation and inhibition of the serotoninergic reactions.