The development of two models of acute inflammation (carrageenan-induced foot oedema and pleurisy) was studied in rats after 1 month of a 0.2 p.p.m. copper-deficient diet and after 5 months of a 0.6-0.8 p.p.m. copper-deficient diet. A 'pro-inflammatory' effect of copper deficiency was observed with the 0.2 p.p.m. diet, whilst no effect was evident following the 0.6-0.8 p.p.m. copper deficient diet. These results are briefly commented upon.