Objective: To elucidate the change in pulmonary blood flow brought about by nitric oxide (NO) inhalation during partial liquid ventilation (PLV). Design: Prospective, controlled study. Setting: A research laboratory at a university medical center. Subjects: Fourteen Japanese white rabbits (3.2 +/- 0.05 kg body weight).Interventions: Animals were mechanically ventilated in the right de cubitus position. Following saline lung lavage, PLV was started with perflubron (15 ml/kg). In the NO group (n = 7), PLV was supplemented by a 30-min challenge of NO inhalation (10 ppm) from 30 min after the initiation of PLV. In the control group (n = 7), PLV was continued for 60 min. Measurements and main results: For the pulmonary blood flow analysis, colored microspheres were administered from the right atrium at 30 min (T-PLV1) and 60 min (T-PLV2) after the initiation of PLV. The percentage of the left lung blood flow in the total pulmonary blood now (% Q(L)/Q(T)) was significantly increased by NO inhalation in the NO group (p = 0.0164), while that in the control group was significantly decreased during the same period (p = 0.0107). PaO2 in the NO group was significantly increased by NO inhalation (p = 0.0153), but not in the control group (p = 0.7911). Conclusion: Inhaled NO during PLV shifted the pulmonary blood now to the non-dependent region and improved pulmonary gas exchange. This result suggested that inhaled NO took effect predominantly in the non-dependent region during PLV.