For over a century it has been assumed that acute pancreatitis represents an autodigestion of the pancreas by its own, physiologically inactive proteases. Whether, how and where digestive proteases are being activated in the pancreas has remained the topic of much controversy and speculation. We review a number of recent studies that have been undertaken to elucidate the mechanisms and identify the initial subcellular localization of this process. These studies suggest that a premature and intrapancreatic protease activation does, indeed, occur early in pancreatitis and can be experimentally induced in vivo and in vitro. Activation begins within minutes of the induction of pancreatitis and is initially confined to cytoplasmic vacuoles at the apical pole of acinar cells. From here trypsin activity as well as its activation peptide are transferred to the cytosol of acinar cells where autodigestion may begin.