The proliferation of pancreatic extracellular matrix, which characterizes chronic pancreatitis, has been analysed using immunohistochemistry. The relationship of matrix components to intraductal precipitates and the presence of serum proteins in precipitates were also studied to investigate the suggestion that ductal permeability increases in chronic pancreatitis. Pancreatic tissue from organ donors was compared with that from patients with chronic calcifying or chronic obstructive pancreatitis. Frozen sections were labeled with monospecific antibodies to collagen types I, III, pro-III and IV, laminin, fibronectin, IgG, IgA, and IgM and then visualized by indirect immunofluorescence. In chronic pancreatitis, interstitial collagens and fibronectin appeared increased and disorganized in both fibrous tissue and areas that appeared histologically normal. Type IV collagen distribution was abnormal and in some sites was present with interstitial collagen. In addition, intraductal precipitates were shown to contain immunoglobulins, and defects were identified in the duct basal lamina associated with precipitates. These results demonstrate that in chronic pancreatitis interstitial collagens are extensively disorganized, the fibrosis possibly being relatively labile. The presence of serum proteins in intraductal precipitates confirms an increase in ductal permeability, and associated defects in the basal lamina appear to define a route via which serum proteins may enter the intraluminal compartment.