There is clearly a role for the measurement of acute phase proteins and other indices of the acute phase reaction but it is equally clear that no one laboratory test is suitable for use in all clinical situations. The choice of acute phase protein measurement depends on the diagnostic sensitivity and specificity of the measurement in the particular clinical situation. The choice of measurement must also include a decision on time of sampling and whether single or serial sampling would be more appropriate. In most situations where acute phase measurement is useful CRP is the assay of choice with alpha 1-antichymotrypsin also being useful in inflammatory bowel disease and other situations where a wider time window is required. The ESR or plasma viscosity can be useful to screen for disease. Cytokine and enzyme-inhibitor complex measurements may be important assays in the future.