Abstract
A big controversy broke out over whether the results of the studies, which altered H5N1 avian flu viruses and made them infectible to ferrets, should be published or not. In this thesis, based on the examination of its circumstances, I considered the necessity to assess such research by risk/benefit and the necessity to establish the appropriate measures from the standpoints of safety, security and research ethics. Especially, in association with such research, pandemic might break out by various causes such as mutations of viruses in nature, leakage of ones in accidents and willful spread of ones by terrorists. It is necessary to fit a wide variety of measures together to cope with it.
