Abstract： Using two-kidney one-clip renal hypertensive (2K1C group), stress-induced hypertensive (neural group), DOCA-salt treated hypertensive (DOCA group) and spontaneously hypertensive rats (SHR group), to investigate the change in AT1A-receptor autoantibodies (AT1A-Aas) during the development of the four types of hypertension. The biological activities of AT1A-Aas were examined. It was shown that the frequency of occurrence and titres of AT1A-Aas increased significantly during the development of hypertension. In the four hypertensive groups studied, the occurrence of AT1A-Aas was most prominent in SHR, 2K1C and neural groups. The biological effects of AT1A-Aas were shown to increase the beating frequency of cultured neonatal myocardial and vascular contractile tension. It is suggested that autoimmune mechanisms are involved the pathogenesis of different types of hypertension and the AT1A-Aas may be one of the mechanisms leading to cardiac hypertrophy.