Aim To investigate the effect of lipopolysaccharide(LPS) on the expression of inducible nitric oxide syn-thetase (iNOS) gene and kinetics of the expression ofiNOS induction in rat heart, aorta and kidney tissues.Methods iNOS mRNA expression was determinedby Northern blot analysis and NOS activities were ob-served by NADPH-diaphorase staining.Results The expression activities of iNOS gene inrat three tissues were undetectable be fore LPS treat-ment. iNOS mRNA in the heart, aorta and kidney be-gan increased at 2 h after LPS treatment, and reacheda peak at 6 h, then decreased gradually and returned tocontrol levels at 24 h. NOS histochemical stainingshowed that there was some expression of constitutivenitric oxide synthetase (cNOS) in rat three tissues un-treated by LPS. NOS activities in the three tissues roseobviously after LPS treatment and still remained thehigher leve1 till 24 h. This result suggested that iNOSis considerably steady in the tissues after it is syn-thetized.Concluslon iNOS mRNA and activities are marked-ly induced by LPS in rat heart, aorta and kidney, andthe kinetics of induction is similar in the three tissues.