Background: Recent experimental findings have suggested that activation of trypsinogen by cathepsin B within acidic pancreatic acinar cell cytoplasmic vacuoles may be a critical early event in both secretagogue and diet-induced pancreatitis. The weak base chloroquine accumulates within acidic intracellular compartments, raises their pH, and can inhibit proteolysis as well as cathepsin B. Methods: We have investigated the effect of in vivo chloroquine administration on both secretagogue and diet-induced experimental pancreatitis to determine if raising the pH of cytoplasmic vacuoles in these models of pancreatitis would have a protective effect. Results: Infusion of chloroquine (5 mg · kg-1 · h-1) resulted in the uptake and concentration of chloroquine in the pancreas, an increase in the pH of acinar cell acidic compartments, and interference with the pH-dependent sorting of lysosomal hydrolases from digestive enzyme zymogens. However, chloroquine administration did not have a protective effect against the hyperamylasemia, the pancreatic edema, the morphological changes or the mortality that is associated with these models of pancreatitis. Conclusions: These observations lead us to conclude that raising the pH of acinar cell acidic compartments by in vivo administration of chloroquine does not prevent either secretagogue or diet-induced pancreatitis.