Trypsinogen and amylase content has been analysed by flow cytometry in individual pancreatic cells from rats with acute pancreatitis induced by pancreatic duct obstruction, from the earliest stages to 48 h after obstruction. Parallel morphological studies of the pancreas by electron microscopy and analysis of various parameters for the diagnosis of pancreatitis will allow research into the possible relationship between intracellular enzyme load and the severity of pancreatitis. Progressive increases in amylase activity in ascites and plasma, the volume of ascites, haematocrit, vacuolization, oedema and macrophage infiltration were observed between 1.5 h and 12 h after duct obstruction. A progressive increase in enzyme content was also observed in individual acinar cells at this stage. Interestingly, the larger increase was for trypsinogen, so that the trypsinogen/amylase ratio was significantly increased in all acinar cells by 12 h after duct obstruction. This represents a risk factor for the development of pancreatitis. Sections of pancreas taken from rats that had duct obstruction for 48 h showed massive dilatation and disorganization of the endoplasmic reticulum, focal apoptosis and necrosis. These severe alterations would affect enzyme synthesis, as reflected by the significant decrease in the intracellular enzyme load observed at this stage. However, not all acinar cells were affected equally by the damage induced by pancreatitis: R(1) cells appeared to be more sensitive than R(2) cells. In conclusion, intracellular accumulation of digestive enzymes occurs at early stages of pancreatitis, and this effect is proportionally greater for trypsinogen, a finding that could explain the degree of severity achieved in the course of pancreatitis.