The aim of this study was to determine whether administration of the non-steroidal anti-inflammatory agent ibuprofen might attenuate the acute-phase response in patients with colonic cancer. Cytokines and acute-phase proteins were measured before administration of ibuprofen and again 3 days later, when protein synthesis was measured using 15N-glycine. In patients with cancer, ibuprofen caused a significant reduction in the plasma concentration of all five acute-phase proteins studied. Although interleukin 6 levels were raised, they did not change following administration of ibuprofen. Unlike the situation in patients with cancer who did not receive ibuprofen, whole-body protein kinetics were similar to those of control subjects in patients with cancer who received ibuprofen. Whether or not ibuprofen had been administered, non-export hepatic protein synthesis rates were significantly lower in patients with than in those without cancer. These results suggest that short-term administration of ibuprofen can attenuate accelerated whole-body protein kinetics and the acute-phase response in patients with advanced cancer.