Understanding of the nitric oxide (NO) role in the pathogenesis of acute and chronic disorders of the pulmonary circulation contributed to the introduction of inhaled NO (iNO) in the complex therapy of patients after lung transplantation. Inhaled NO can form methemoglobin (MetHb) and nitrate. The aim of the study was to investigate the relationship between iNO and nitrite/nitrate (NOx) and MetHb levels in the blood serum of 7 patients after lung transplantation. Duration of iNO therapy was 3 ± 1 days, the data were reviewed at 1 to 10 days after transplantation. Patients showed a significant increase of the NOx levels from day 1 to 5 after surgery, meanwhile the MetHb levels remained within the normal range. The significant positive correlations were found between the iNO use and NOx concentrations, between iNO use and MetHb levels, and between NOx and MetHb levels. The obtained results suggest that the iNO use in lung transplant recipients requires a close monitoring of the administered iNO concentration and the blood levels of MetHb and NOx.