The stable-isotopic composition of nitrogen (δ15N) or carbon (δ13C) of body tissues depends on the isotopic composition of food sources and on shifts due to isotopic fractionation during metabolism. As little is known about the effects of pathophysiological conditions we measured δ15N and δ13C values in hair and hair amino acids of patients with cirrhosis (n = 21) and compared the results with those of healthy subjects (n = 100) randomly selected from the 1987–1988 VERA German nutrition survey population. Cirrhosis was reflected in lower hair 15N abundances (6.7 vs. 9.9‰ δ15N; P <0.001) whereas hair 13C abundances did not differ from healthy subjects (−19.4 vs. −19.6‰ 13C). Distinct patterns of δ15N and δ13C values were measured in hair amino acids. The δ15N values of phenylalanine were significantly higher in cirrhotics (P < 0.001). With the exception of isoleucine, threonine, and proline all other measured amino acids showed lower δ15N values than healthy subjects (P < 0.001). Lower hair δ15N values were associated with cirrhotic liver disease which suggests that under this condition the altered liver amino acid metabolism affects the nitrogen isotopic composition of the amino acids used for hair protein synthesis. It remains to be determined in controlled studies whether the altered nitrogen isotopic composition directly reflects the pathophysiological condition or is related to differences in dietary protein intake from plant or animal food sources. Copyright © 2006 John Wiley & Sons, Ltd.