There have been few reports on the preservation of viruses at the temperature of liquid nitrogen (-196 C). In this study, factors affecting the survival of phage were observed. Phage lysates in broth did not lose titer after a storage period of 4 weeks in liquid nitrogen. The rate of freezing was not critical, but freezing in nitrogen vapor was not satisfactory. When the virus was partially purified and suspended in buffered saline solution, it rapidly lost titer. Of seven protective agents recommended in the literature, only gum acacia seemed to demonstrate significant protection of purified virus against loss of viability. The temperature of thawing of phage suspended in broth did not affect its titer after freezing and storing in liquid nitrogen.