Localization of phospholipase A₂, lipase and colipase immunoreactivity were studied in paraffin embedded tissue sections. The samples were taken from the pancreas of 12 patients suffering from acute haemorrhagic necrotizing pancreatitis, and from diseased adipose tissue of 7 patients suffering from traumatic mammary fat necrosis. Peroxidase‐antiperoxidase immunohistology revealed consistent positive reaction against phospholipase A₂, lipase and colipase at the border of fat necrosis in pancreatic interlobular adipose tissue and in peripancreatic, mesenterial and retroperitoneal fat. The fat necroses of the breast were devoid of reaction. The results support the idea that in addition to lipase colipase and phospholipase A₂ participate in the development of fat necrosis in acute pancreatitis. Pancreatic lipolytic enzymes are not present in the adipose tissue in mammary fat necrosis.