We investigated the role of neutrophils and the involvement of apoptosis in cerulein-induced acute pancreatitis. Male Sprague-Dawley rats were divided into 2 groups. In the control group, acute pancreatitis was induced by subcutaneous injections of cerulein. In methotrexate-treated group, the rats received intraperitoneal injections of methotrexate to produce neutrophil depletion before the injections of cerulein. The rats were sacrificed at the indicated time points until 72 h after the first injection of cerulein. Neutrophil depletion ameliorated pancreatic edema and vacuole formation in acinar cells during the early stages of cerulein-induced acute pancreatitis. Electron microscopy, DNA gel electrophoresis and in situ nick end-labeling revealed the involvement of apoptosis in acinar cells in cerulein-induced acute pancreatitis. Furthermore, the number of apoptotic acinar cells in neutrophil-depleted rats showed an about 2-fold increase during the late stages when compared with those in the control rats. Our results suggest that neutrophil depletion in cerulein-induced pancreatitis leads to amelioration of pancreatic injury during the early stage, and enhancement of apoptosis by neutrophil depletion occurs during the late stage.