Spontaneously Hypertensive Rats (SHR) are the most extensively used animal model for genetic hypertension, increased stroke damage and insulin resistance syndromes, however the identification of target genes has proved difficult. SHR show elevated sympathetic nerve activity, and stimulation of the central blood pressure control centres with glutamate or nicotine results in exaggerated blood pressure responses, effects that appear to be genetically determined. Kynurenic acid, a competitive glutamate antagonist and a non-competitive nicotinic antagonist, can be synthesised in the brain by the enzyme Kynurenine Aminotransferase-1 (KAT-1). We have previously shown that KAT-1 activity is significantly reduced in SHR compared to normotensive Wistar Kyoto rats (WKY). Here we show that KAT-1 contains a missense mutation, Glu61Gly, in all the strains of SHR examined but not in any of the WKY or outbred strains. Previous studies on F2 rats from a cross of stroke prone SHR and WKY have shown a suggestive level of linkage between elevated blood pressure and the KAT-1 locus on chromosome 3. In addition, the mutant enzyme expressed in E. coli displays altered kinetics. This mutation may explain the enhanced sensitivity to glutamate and nicotine seen in SHR, which may be related to an underlying mechanism of hypertension and increased sensitivity to stroke.