Male, Wistar rats were injected into the right lateral ventricle of the brain with 250 ~g of 6-hydroxy-dopamine (6-OHDA). The behaviour of animals and the level of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) were measured after different periods of time. During the first hour after 6-OHDA injection the behaviour of rats was similar to that observed after reserpine or a benzoquinolizine derivative; 6 h after the drug injection signs of sedation occurred. 24 and 48 h after 6-OHDA treatment locomotor activity of rats was similar to the activity of untreated animals. 68 h after 6-OHDA application a decrease of exploratory activity was noted. 7 h after 6-OHDA treatment a decrease of NA level was observed in the cortex, meseneephalon, thalamus and hypothalamus but an increase of NA content in the striatum. 3 days after 6-OHDA injection a decrease of the NA content in the cortex, thalamus and hypothalamus was seen. The DA level increased in most of the examined areas 7 h after 6-OHDA application; 3 days after the drug injection the DA level decreased in hypothalamus, thalamus and striatum and did not change in other brain areas. The 5-HT level increased in the pens and medulla oblongata and decreased in the mesencephalon 7 h after 6-OHDA injection and was unchanged in all examined structures 3 days after 6-OHI)A application. These biochemical changes in the brain were not correlated with the behavioural changes of rats.