It is well known that the continuous irrigation method is effective to control the pyogenic osteomyelitis. However, there are no reports concerning the period of continuous irrigation method as to how long the method is applied for treating the pyogenic osteomyelitis. Some authors have determined its period depending on patient's conditions, characteristics of draining fluid and results of bacterial culture. Therefore, this experiment was performed to determine the physiological or pathological effects of the continuous irrigation to the normal bone and the time when the effects to normal bony tissue happened. In author's tudy, 30 house rabbits are used for determining the period that the normal bone is pathologically changed by experimental continuous irrigation method. The continuous irrigation in normal femoral shaft bone of rabbit set up dead bone formation began at the early of 5 weeks so in diseased bone such as osteomyelitis is the period of the continuous irrigation may be shorter than that of normal bone. I assumed that the period of the continuous irrigation sustaining 4 week-duration may not be occurred any problems to bony tissue.