A morphological examination was performed on megakaryocytic emperipolesis containing neutrophils in the rat bone marrow induced by intravenous administration of lipopolysaccharide (LPS). Ultrastructurally, the engulfed neutrophils appeared to lie in the demarcation membrane system (DMS) of megakaryocytes. Intact neutrophils generally migrated from DMS into the lumen of vascular sinus across the endothelium of sinus wall. However, some neutrophils showed characteristics of apoptosis, and DNA fragmentation was detected in these cells by the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling method. Thus, the cell death of neutrophils engulfed by megakaryocytes was thought to be apoptosis. The present results suggest that megakaryocytes contribute to random selection of an excess of neutrophils in the bone marrow of rats treated with LPS.