Inflammation and injury to tissue results in a variety of local and systemic events, however although the local events of oedema formation and cellular infiltration have received considerably more attention the systemic response to inflammation is no less profound. The particular systemic event which forms the substance of this communication is the change in the circulating levels of plasma proteins which occurs after inflammatory injury, and the manner in which these changes in plasma concentration are controlled by changes in plasma concentration are controlled by changes in the rate of synthesis. A discussion of the role of the liver in controlling inflammatory events, in relation to the synthesis of an anti-inflammatory protein has been given; the present work is an extension of this and describes the changes in concentration and synthesis rate of albumin, fibrinogen and alpha1 acid glycoprotein during adjuvant arthritis in the rat. The changes which occur are regulated at the liver by alteration of the rate of synthesis of the individual protein. For example albumin at the height of adjuvant arthritis falls to a third of its normal plasma level whereas the level of alpha1 acid glycoprotein increases up to twenty-fold; these changes are reflected by similar changes in their synthesis rate by the liver. The effect of the fall in albumin concentration on the plasma binding of anti-inflammatory drugs (and their toxicity) in relation to these findings will be discussed along with the biological role of the acute phase plasma proteins and hence the influence of the liver in the response to injury.