In this study, we have observed the effect of L-arginine(L-arg) and omega N-nitro-L-arginine (LNNA) on the contractile-relaxation response and the cGMP level in arterial strip using the model of rat thoracic aorta with endothelial injury and neointimal formation. Organ chamber experiment and radioimmunoassay showed that, the 3rd day after endothelial injury of the rat thoracic aorta, their endothelium-dependent relaxtion response caused by L-arg, as well as endothelium dependent contractile response caused by LNNA were impaired seriously, basic cGMP reduced obviously, and the change of cGMP caused by L-Arg and LNNA was impaired markedly. On the 10th day after injury a pronounced recovery was noticed, and 21st day, the situation was further improved, but could not restore completely. The results indicate that the production of EDRF in the rat thoracic aorta after endothelial injury may be impaired seriously, and could not recover completely for a longer time.