With the use of in vitro receptor autoradiography, this study aims at determining whether the higher level of kinin B₂ receptor density in the spinal cord of the spontaneously hypertensive rat (SHR) is secondary to arterial hypertension and whether chronic treatment with angiotensin I-converting enzyme inhibitors (ACEI) can regulate neuronal B₁ and B₂ receptors. SHR received, from the age of 4 wk, one of the two ACEI (lisinopril or zofenopril, 10 mg · kg¹ · day¹) or for comparison, the selective AT₁ antagonist (losartan, 20 mg · kg¹ · day¹) in their drinking water for a period of 4, 12, and 20 wk. Age-matched untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. B₂ receptor binding sites in most laminae were higher in SHR than in WKY from the age of 8 to 24 wk. Whereas B₁ receptor binding sites were significantly present in young SHR and WKY, they were barely detectable in adult rats. ACEI (16 and 24 wk) and AT₁ antagonist (24 wk) enhanced the number of B₂ without changing B₁ receptor binding sites. However, at 8 wk the three treatments significantly increased B₁ and decreased B₂ receptors in lamina I. It is concluded that 1) the higher density of B₂ receptors in the spinal cord of SHR is not due to hypertension, 2) kinin receptors are regulated differently by ACEI in neuronal and vascular tissues, and 3) aging may have a profound impact on levels of B₁ and B₂ receptors in the rat spinal cord.