This study was designed to estimate the ability of squalene treated mice to eliminate systemically infected bacteria and fungi and to elucidate the mechanism. As a result of measuring the ability to remove systemically infected bacteria and fungi, The ability of mice to remove the organism was found to increase in squalene treated mice when compared with control mice. And also the ability of phagocytic cells to produce Reactive Oxygen Intermediate(R.O.I.) increased in squalene treated mice. When the NADPH oxidase activity that make R.O.I. produce was measured, the activity increased in squalene treated mice, too. Therefore the good clearance of live organism in squalene treated mice is likely to relate to phagocytic cell activation. The activation of phagocytic cells might be mediated via the increased production of R.O.I. due to the increase of NADPH oxidase activity.