Acute pancreatitis is characterized morphologically by edema, hemorrhages, parenchymal necrosis and fat necrosis. The inflammation is accompanied by infiltration of polymorpho-nuclear leukocytes. According to the absence or presence of necrosis the disease can be divided into interstitial (or edematous) pancreatitis and hemorrhagic-necrotizing pancreatitis. The severity of disease can be graded in the histological sections either by giving scores to the different types of morphological alterations or by determining the proportion of necrotic tissue of the total lobular parenchyma. The former method is based on subjective assessment of histological slides and is suitable for the evaluation of both edematous and necrotizing pancreatitis. Histometric measurement of necrotic parenchyma can be used only in the necrotizing forms of experimental pancreatitis, e.g. in those induced by intra-ductal injection of bile, bile salts or digestive enzymes, and in the dietary ethionine-induced pancreatitis. Grading of the tissue damage is essential when the effects of different therapies are evaluated.