To investigate the possible relation between changes in behaviour and the development of hypertension in the spontaneously hypertensive rat (SHR), the effect of intracerebroventricular (ICV) administration of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) on blood pressure and spontaneous behaviour was studied. In addition to an attenuation of the rise in blood pressure in SHR, 6-OHDA induced a marked decrease in rearing activity in the open field towards levels found in WKY. Other parameters were either not changed (stereotyped sniffing) or influenced in a comparable way in SHR and WKY (increase in locomotion). These results suggest that ICV 6-OHDA may simultaneously affect the development of hypertension and certain components of the changed behaviour of SHR. The exact relation between the two phenomena awaits further investigation.