Carrageenan-induced hind paw oedema has been studied in rats deprived of copper for different lengths of time. A common feature observed in normally fed and copper-deficient rats was the rise of serum copper levels occurring between 10 and 24 h after the injection of the irritant. After 1 month of copper-deficient diet no differences are seen in the oedema developed by controls and copper-deprived animals, while after 3 months the oedema developed by copper-deficient rats was significantly greater compared with the controls.