Hypertension produces pathophysiological changes that are often responsible for the mortality associated with the disease. It is evident that overactive renin-angiotensin systems play a central role in the development of hypertension and target organ damage associated with hypertension. We have previously found that a novel angiotensin II receptor (AT1) vaccine-ATR12181 attenuated the development of high blood pressure (BP) in spontaneously hypertensive rat (SHR) model of human essential hypertension. Our objective was to determine whether this attenuation of high BP is associated with prevention of target organ damage induced by hypertensive state. SHRs were immunized against a peptide (coded ATR12181) from the extracelluar portion of the AT1A receptor by repeated subcutaneous injections of peptide-tetanus-toxoid complex in combination with Freund's adjuvant. A 64 weeks long-term observation was performed. Repeated vaccinations resulted in the induction of anti-ATR12181 antibodies. At the end of observation, vaccinated SHRs manifested lower BP, decreased cardiac hypertrophy and attenuation of kidney injuries. mRNA levels of c-fos and c-jun in heart and kidneys were decreased in vaccinated SHRs. Since a self antigen was used, safety of vaccine was concerned. However, the signs of autoimmune diseases were not observed in the sections of heart and kidney. These data demonstrated that repeated immunization against a domain of the extracellular portion of the AT1 receptor was able to cause a target organ protection against hypertension. Active immunization against the AT1 receptor may be considered as a promising new strategy in the treatment of hypertension.