Fresh frozen plasma (FFP) has been proposed as a specific therapy for acute pancreatitis. It may replenish important circulating proteins, particularly the naturally occurring anti-protease system. To investigate this potential therapy, 72 patients with predicted severe disease were selected from 301 admissions with acute pancreatitis using the modified Glasgow prognostic scoring system. They were randomised within 6 h of diagnosis to receive FFP (8 units daily for 3 days) or a similar volume of colloid control as part of their intravenous fluid therapy. Clinical progress was monitored and specific blood proteins were measured on days 1, 3 and 7. FFP therapy significantly increased the day 3 concentrations of some of the acute phase proteins (C1-reactive protein P less than 0.02, D-dimer P less than 0.05 and fibrinogen P less than 0.05) as well as some proteins which showed a fall in circulating concentration during the early stages of the disease (alpha 2 macroglobulin P less than 0.001, antithrombin III P less than 0.01 and fibronectin P less than 0.001). However, there was no significant difference between the two groups in terms of clinical outcome. Mortality was 20% in patients who received FFP and 18% in the colloid control group. Despite the ability of FFP therapy to supplement circulating concentrations of several potentially useful proteins during acute pancreatitis, it does not appear to improve clinical outcome.