In a series of patients with acute pancreatitis we have studied complement factors, antiproteases (alpha 2-macroglobulin and alpha 1-antiprotease) and C-reactive protein to determine the value of their sequential measurement in the prediction of outcome relative to clinical assessment and current multiple factor scoring systems. Complement factors were unhelpful in predicting the severity of an attack. alpha 2-Macroglobulin levels were significantly lower in complicated attacks during days 3-8 and alpha 1-antiprotease levels were significantly higher during days 4-8. C-reactive protein concentrations showed the best discrimination between mild and complicated attacks, levels rising higher and persisting for longer in complicated attacks; these differences were highly significant from day 2 (the morning after admission) to day 8. The concentrations providing the best discrimination were found to be greater than or equal to 210 mg/l for the peak C-reactive protein (on the second, third or fourth day) and greater than or equal to 120 mg/l for the C-reactive protein at the end of the first week. Analysis demonstrated both the peak or seventh-day C-reactive protein concentration to be of similar accuracy to either the Ranson or Glasgow multiple factor scoring systems and slightly better for attacks associated with gallstones. The C-reactive protein assay is simple, quick to perform, provides useful clinical information and is more likely to be of value and to be adopted into routine clinical practice than multiple factor scoring systems.