The aim of this study was to analyze, using electron microscopy, the morphological alterations that progressively appear in the pancreas of rats with acute pancreatitis induced by bile-pancreatic obstruction over 48 h. In addition, in order to ascertain the capability of pancreas regeneration at different stages of pancreatitis, the distribution of pancreatic cells throughout the different phases of the cell cycle was also analyzed by flow cytometry using propidium iodide staining. Interstitial edema, macrophage infiltration, vacuolization, and dilatation of endoplasmic reticulum were observed from 1.5 h after obstruction onward. Interestingly, cell cycle studies showed an increased proportion of S-phase cells at early stages of pancreatitis (1.5 h after obstruction), which leads to a significant increase in cells in G2/M phase 12 h after pancreatic obstruction. Histological studies revealed severe alterations in pancreas of rats with obstruction maintained over 48 h which affects the nuclear structure. Intracellular disorganization, apoptosis, and focal necrosis were observed at this stage. Furthermore, flow-cytometric analysis of cell DNA contents showed a significant decrease in the proportion of S and G2/M cells and a significant increase in G0/G1 cells, suggesting an arrest of almost all cells in quiescent states. These results suggest that rat pancreas cells are able to recover during the first 12 h after pancreatic obstruction. However, the gland would lose its ability to regenerate if the obstruction was maintained for longer periods.