im To determine the effect of endothelin on highblood pressure and myocardiac hypertrophy.Methods We observed endothelin levels in plasma,and endothelin levels, gene expressions of endothelinand endothelin A receptor in left ventricle (LV) of 5,14, 26 week-old spontaneously hypertensive rats(SHR) and age-matched normotensive Wistar Kyoto(WKY) rats with radioimmunoassay and Northern blothybridization.Results Plasma endothelin levels were not significant-ly different between SHR and WKY rats. LV en-dothelin concentration, endothelin, endothelin A re-ceptor gene expressions increased only in 26 week-oldSHR.Conclusion Endothelin does not play an etiologic rolein myocardiac hypertrophy in SHR, but may play arole in the development of hypertension and the inifia-tion of its complications.