Many of the metabolic sequelae to infection and inflammation, such as fever, trace mineral redistribution, skeletal muscle catabolism, and the acute-phase protein response, are mediated by leukocytic pyrogen (interleukin 1). In the anterior hypothalamus and in skeletal muscles leukocytic pyrogen appears to induce the synthesis of prostaglandin E2 which mediates fever and skeletal protein catabolism. It is unclear whether any additional metabolic responses to leukocytic pyrogen result from prostaglandin production. This study was undertaken to investigate the ability of ibuprofen, a specific cyclooxygenase inhibitor, to alter protein and trace metal responses to leukocytic pyrogen or endotoxin when given in quantities sufficient to block the febrile response. In guinea pigs given continuous infusions of leukocytic pyrogen or endotoxin, a 0.6 to 0.8 degrees C fever was observed within 4 h, and zinc and iron concentrations in serum fell by 63 to 78% (P less than 0.01). Rates of whole body amino acid appearance, oxidation, and incorporation into protein were all significantly increased by leukocytic pyrogen and endotoxin treatment, (P less than 0.05) as were the fractional hepatic and seromucoid protein synthesis rates in leukocytic pyrogen-treated animals (P less than 0.01). Muscle protein synthesis was unchanged. Although pretreatment with infusions of ibuprofen completely ablated the febrile response to leukocytic pyrogen and endotoxin, decreases in zinc and iron concentrations in serum and leukocytosis were unaffected. Overall increases in whole body amino acid kinetics induced by leukocytic pyrogen or endotoxin were only minimally affected by ibuprofen. We concluded that treatment with prostaglandin synthesis inhibitor ibuprofen did not affect whole body trace metal, hematological, or hepatic acute-phase-induced responses to leukocytic pyrogen or endotoxin, either because these responses are prostanoid independent or because they are only partially mediated by eicosanoid products.