A consecutive series of 239 patients experiencing 336 separate attacks of acute pancreatitis have been treated with fresh frozen plasma during the first 5 days of the illness. Using established criteria, 96 attacks occurring in 69 patients were judged to be severe at the time of admission. The overall mortality was 3.7 per cent per patient population and 2.7 per cent per total number of separate attacks. Four of 69 patients with severe pancreatitis (5.8 per cent) have died and the mortality rate for the 96 severe attacks was 4.2 per cent. No complications which could be directly attributed to fresh frozen plasma were encountered in the series. The results of this prospective pilot study with naturally occurring human proteinase inhibitors have been encouraging and indicate the need for randomized clinical trials.