Introduction: The concentration of carboxypeptidase B activation peptide (CAPAP) is proposed to be a predictor of severe acute pancreatitis. The activated protein C (APC)-protein C inhibitor (PCI; APC-PCI) complex in plasma could be useful in detecting the hypercoagulative condition in severe acute pancreatitis. Method: In this prospective study, mild (n = 50) and severe (n = 9) cases of acute pancreatitis were compared with respect to levels of CAPAP and APC-PCI, and sorted in time intervals from onset of symptoms to sampling. The peak values of the C-reactive protein (CRP) within the 1st week were also compared. Results: CRP detected the severe cases with a sensitivity of 0.89 and a specificity of 0.74 (cut-off level 200 mg/l). In the interval 0-72 h, CAPAP could predict the severity of the disease in serum and urine (sensitivity 0.52/0.29, specificity 0.73/0.93, cut-off 2 nM/60 nM). The level of APC-PCI in plasma could predict the severe condition in the interval 0-24 h after the onset of symptoms (sensitivity 0.6, specificity 0.66, cut-off level 0.54 mug/l). Conclusion: Of the parameters explored, CRP is still the best biochemical marker to distinguish between severe and mild acute pancreatitis. CAPAP could be useful in combination with other tests, but the APC-PCI complex's diagnostic time interval is too short to be used in the clinical routine. and IAP.