Pancreatic tissue fluid pressure and pain were compared in a longitudinal study in nine patients undergoing drainage operations for pain in chronic pancreatitis. Pressure measurements were performed percutaneously before the operation, intraoperatively before and after the drainage procedure, and percutaneously at follow-up study 1 year after the operation. The pressures were compared with 2-week pain scores. The median predrainage pressures were increased (27 mm Hg; range, 19-34 mm Hg; normal, 7 mm Hg; range, 2-13 mm Hg). The drainage operations led to a 45% pressure decrease (range, 0-77%). At 1-year follow-up study the pressure was increased in the patients with recurrent pain, and there was a significant relation between pressure and pain (R = 0.85, p less than 0.02). Furthermore, patients with an intraoperative pressure decrease greater than 10 mm Hg had a pain-free postoperative period. The duration of the pain-free period was significantly related to the size of the intraoperative pressure decrease (R = 0.79, p less than 0.03). These results further suggest that there is a causal relationship between pancreatic tissue fluid pressure and pain in chronic pancreatitis and that the success of the drainage procedure may be predicted by intraoperative pancreatic tissue fluid pressure measurements.