The ability to desiccate mammalian cells while maintaining a high degree of viability would have implications for many areas of biological science, including tissue engineering. Previously, we reported that introduction of the genes for trehalose biosynthesis allowed human cells in culture to be reversibly desiccated for up to 5 days. Here, we have further investigated the factors that allow human cells to survive in the desiccated state. The most important finding is that vacuum greatly enhances the ability of human cells in culture to withstand desiccation. In fact, cells dried slowly and stored under vacuum are able to withstand desiccation even in the absence of added carbohydrates or polyols. In addition to vacuum, the rate of desiccation, the temperature at which cells are maintained, the degree of confluence when dried, and the presence or absence of light have a large effect on the ability to retain viability in the desiccated state. Our data are consistent with a model in which cells can retain viability if they are desiccated in such a way that cellular structures are maintained. However, gradual loss of viability may be due to damage that occurs over time in the desiccated state, perhaps due to free radicals. Further optimization of the process for desiccating and maintaining cells is required before long-term storage of desiccated cells can be achieved.