The late phase of severe septic shock is associated with reduced cardiac output (CO) and activation of the inducible isoform of nitric oxide synthase (NOS). This study examined the effects of 1400 W (N-3-aminomethyl-benzyl-acetamidine), a new selective inhibitor of inducible NOS (iNOS), relative to those of N(G)-nitro-L-arginine (L-NNA, non-selective inhibitor of NOS) and the vehicle, on mean arterial pressure (MAP), CO, total peripheral resistance (TPR) and tissue blood flow (BF) in thiobutabarbital-anesthetized rats with lipopolysaccharide (LPS, 10 mg/kg, i.v.) induced endotoxemia. At 2.5 as well as 4 h after injection of LPS, MAP, CO, and BF of the stomach, skeletal muscle and skin were decreased, but TPR was increased, BF to the heart and kidneys were also decreased at 4 h after injection of LPS. Treatment of endotoxemic rats with 1400 W (3 mg/kg followed by 3 mg/kg/h, i.v.) at 2.5 h after endotoxin challenge prevented the late phase fall in MAP without exacerbating the decreases in CO and tissue BF. In contrast, treatment with L-NNA (8 mg/kg followed by 3 mg/kg/h, i.v.) at 2.5 h did not prevent the decline in MAP in the LPS-treated rats. Furthermore, CO drastically decreased, TPR markedly increased, and BF to the heart, brain, intestine and skeletal muscle were decreased at 4 h relative to the readings in saline- or 1400 W-treated endotoxemic rats. Therefore, selective inhibition of iNOS by 1400 W restores MAP without compromising CO, but non-selective inhibition of NOS is detrimental at the late stage of septic shock.