Background: The aim of this study was to investigate the potential effects of liver insufficiency on nitric oxide concentrations in exhaled air. Methods: Nitric oxide concentrations in the exhaled air from 13 patients with liver cirrhosis and 11 healthy control subjects was examined by the single-breath technique. Results: There was a clear correlation between Child-Pugh score and NO in exhaled air (peak after 15 sec of breathholding, R = 0.623, P = 0.023). Similarly, there were significant correlations in peak NO concentrations and alkaline phosphatase, bilirubin, aspartate and alanine aminotransferase, and albumin. The most severely ill patient in our study had the highest NO concentrations in her exhaled air. On recovery from her liver illness the concentration of NO in her exhaled air decreased. There was no correlation between circulating levels of the endogenous NO synthase inhibitors asymmetric and symmetric A^G.A^G-dimethyl -arginine and exhaled NO concentrations. Conclusions: The present data show a correlation between endogenous NO formation in the respiratory system and liver dysfunction. This might contribute to the understanding of the pathophysiology in pulmonary vasodilatation in liver disease.