A study has been undertaken on the relative merits of a variety of acute phase proteins in the assessment of patients with inflammatory conditions. Five acute phase proteins (alpha 1-antitrypsin, alpha 1-antichymotrypsin, orosomucoid, haptoglobin and C-reactive protein) and the ESR were measured in 171 patients presenting to the gastroenterologists (gastrointestinal disease: 130, other disease: 41). Assessment of the sensitivity and specificity of the proteins and the ESR showed alpha 1-antichymotrypsin to be the most sensitive test (95%) with specificity (81%) similar to the other acute phase proteins measured. Factors such as oestrogens, renal failure and genetic variants affected the value of alpha 1-antitrypsin, orosomucoid and haptoglobin. In the routine protein laboratory the combination of a 'short' half-life and 'long' half-life protein is likely to offer the most useful screen for inflammation in samples obtained from a wide range of patients. The two acute phase proteins C-reactive protein and alpha 1-antichymotrypsin fulfil these criteria.