Fig. 2. Changes in plasma methemoglobin level after breathing nitric oxide at ascending concentrations for 15 min at each nitric oxide level after infusion of HBOC-201 (12 ml/kg) in awake lambs (n = 4). * P < 0.05; differs from the changes in methemoglobin level induced by breathing 0.5 ppm nitric oxide for 15 min. HBOC = hemoglobin-based oxygen-carrying solution.