An application of stable isotope distribution of bioelements to ecogeochemical and archaeological studies requires precise knowledge on the relationship between available field samples and diet. As the nature of birds makes it possible to set up an isotopically well defined experiment, nitrogen and carbon isotope relationships between various tissues of a cormorant and its constant diet was studied. The tissues were collected after more than 23 years on the same diet. The two stable isotope ratios for the diet and the tissues showed a high correlation (r = 0.92). The linear regression analysis gave the slope of 1.1. Among the tissues examined, skin showed the highest enrichment in both15N (4.8‰) and13C (4.2‰), while brain gave the lowest enrichments (0.8‰ for15N and 1.1‰ for13C).