Apoptosis is now widely recognized as a common form of cell death and represents mechanism of cell clearance in many physiological situations where deletion of cells is required. In vivo administration of bacterial lipopolysaccharide (LPS) to Balb/c mice induced DNA fragmentation in the thymus. DNA fragmentation in the thymus was roughly dependent on the dose of LPS injected and reached the peak 18 hours after injection. This apoptosis in the thymus might be mediated due to LPS stimulant. DEN (diethylnitrosamine) has been shown to cause liver cancer in experimental animals and humans. The hepatic tumorigenesis was induced by ad libitum feeding of DEN only. It was suggested that DEN induced hepatic tumorgenesis in rat is a good reproducible model for studying biochemical and pathophysiological changes associated with the development of hepatic tumorigenesis and apoptosis.