Pancreatic microvasculature in cerulein-induced pancreatitis was studied at the electron and light microscopic level. Using a modified model of in situ india ink perfusion, focally a marked reduction of the number of india-ink-filled microvessels was found. The numerical density (NA) of filled microvessels was reduced by 66.7% in pancreatitis. The morphological correlate for this extreme numeric reduction might be a collapse of the lumen of pancreatic microvessels. In the presence of cerulein pancreatitis 42% of pancreatic capillaries had a collapsed lumen as shown by electron microscopy. The endothelium of capillaries in acute pancreatitis demonstrated surface blebbing, the formation of cytoplasmatic vacuoles, edema, and swollen mitochondria. Some capillaries had irregularities at the interendothelial junction, and the majority of examined vessels were surrounded by marked perivascular edema. No strict correspondence between histological signs of pancreatitis and light microscopic and/or ultrastructural microvascular alterations could be demonstrated. Our study emphasizes that alterations of microvasculature are present early in experimental edematous pancreatitis. Therefore, alterations of pancreatic microcirculation seem to be of great importance in the pathogenesis of pancreatic inflammation, and should be the subject of further studies.