In the past few years, genotype influence on the occurrence and developmental course of acute pancreatitis is ever more frequently accounted for. Forty-three patients presenting mild (2), medium-severe (33) and severe (6) form of the disease are covered by the study, undertaken with the purpose to assay the role played by some immunoglobulins and polymorphic plasma proteins in this particular disease. In evaluating plasma proteins a deficit of the protease inhibitor Alpha1 antitrypsin is found in twelve patients. However in two cases only Alpha1 antitrypsin deficit is associated with deficiency of the other protease inhibitor--the Alpha2 macroglobulin. In acute pancreatitis patients a genetically determined deficit of protease inhibitory activity is documented, considered a good reason to undertake conservative management using protease inhibitors in the initial phases of the condition.