Weight loss and impaired nutritional status are associated with increased complications following surgery. This study aimed to assess the effect of nutritional status on the magnitude of the acute phase protein response, and determine if this is associated with changes in the magnitude of the related cytokine responses. Nineteen patients (10 wellnourished, 9 malnourished on the basis of body composition) undergoing major abdominal surgery were studied by frequent blood sampling in the early postoperative period. There was a significant reduction in the plasma C-reactive protein response in the malnourished group, but no difference between the groups in the responses of alpha 1-antitrypsin, alpha 1-acid glycoprotein, or in the trace elements iron or zinc, which reflect induction of ferritin and metallothionein. There was an early increase in IL-6, soluble receptors of TNF, and in IL-1 receptor antagonist in both groups, but no detectable increase in plasma IL-1 or TNF. There was no difference between the wellnourished and malnourished group for any of these markers of activation of the cytokine network. Weight loss is therefore associated with a reduction in aspects of the acute phase response, but this is due to impaired effectiveness rather than reduced magnitude of the cytokine response.