The fatty acid profile of hepatic lipid in spontaneously hypertensive rats (SHR)/NDmcr-cp (cp/cp) rats (SHR/NDcp), which offer an animal model of the metabolic syndrome, was characterized by comparing those in Wistar Kyoto rats (WKY), SHR, stroke-prone spontaneously hypertensive rats (SHRSP) and SHR/ NDmcr-cp ( / ) rats (SHR/ND ) . Hierarchical clustering analysis revealed that SHR/NDcp and the other four strains and/or substrains of rats were clearly disparate in fatty acid profile of hepatic lipid and that the disparity observed was due to the drastic increases in the mass of monounsaturated fatty acids, especially palmitoleic acid and oleic acid, in the liver of SHR/NDcp. Activities of stearoyl-CoA desaturase (SCD) and palmitoyl-CoA chain elongase in hepatic microsomes of SHR/NDcp were markedly higher than those of WKY, SHR, SHRSP and SHR/ND . Activities of palmitoleoyl-CoA chain elongase in the liver of SHR/ NDcp were also higher, but to a lesser extent. mRNA levels of SCD1 and elongation of very long-chain fatty acids (Elovl6), but not Elovl5, in the liver of SHR/NDcp were remarkably higher than those of the other four groups of rats. These results suggest that the enhanced expressions of SCD1 and Elovl6 induced abnormalities in fatty acid profile in the liver of SHR/NDcp. Key words fatty acid profile; palmitoleic acid; oleic acid; liver; SHR/NDmcr-cp (cp/cp) rat Obesity, hypertension, hyperlipidemia and hyperglycemia are risk factors for cardiovascular diseases. Patients who have two or more of these risk factors are susceptible to cardiovascular diseases; these states are called the metabolic syndrome. To explore protection against and treatment of the metabolic syndrome, studies on the pathophysiology and metabolic consequences of the metabolic syndrome are required using pertinent animal models. Spontaneously hypertensive rats (SHR)/NDmcr-cp (cp/cp) rats (SHR/NDcp) spontaneously develop obesity and hypertension, and display dyslipidemia and hyperglycemia, the values of body weight, systolic blood pressure, serum triglyceride and blood glucose in SHR/NDcp being 1.43, 1.65, 25.4 and 1.25 times, respectively, compared with those in Wistar Kyoto rats (WKY) (control rats) at 19 or 20 weeks of age.1) Thus, they provide a useful model of the metabolic syndrome.2,3) Hypertensive rats that spontaneously developed as a colony from normotensive WKY, were named SHR.4) By crossing SHR with Sprague-Dawley (SD) rats, obese spontaneously hypertensive rats, Koletsky strain, were obtained; this strain of rats is heterozygous for the cp gene.5) To eliminate the noncorpulent genes of the Koletsky strain, the rats were mated with SHR, and a congenic rat strain (SHR/National Institutes of Health (NIH)-corpulent) was developed.6) SHR/NDcp are a substrain of SHR/NIHcorpulent rats. With regard to metabolic abnormalities as to hypertension, hyperinsulinemia and hyperglycemia in SHR/ NDcp, many studies have been conducted. On the other hand, information on dyslipidemia in SHR/NDcp is very limited.