Six-hydroxydopamine (6-OH-DA) was administered intraventricularly to 6-week-old and 5-month-old spontaneously hypertensive rats (SHR), and was administered into the spinal cord of 6-week-old SHR. Intraventricular administration of 6-OH-DA into 6-week-old SHR prevented the development of hypertension for at least 12 weeks; pressor response of the perfused hindquarters to noradrenaline was the same in 6-OH-DA-treated and vehicle-treated animals. Intraventricular administration of 6-OH-DA into 5-month-old SHR with established hypertension produced only a transient fall in blood pressure. Local injection of 6-OH-DA into the spinal cord produced a marked reduction only in spinal cord noradrenaline but did not affect the development of hypertension in SHR. These findings suggest that brain adrenergic neurons may participate in the development of hypertension in SHR but noradrenergic projections in the spinal cords are not essential for this process.