We report that the introduction of low concentrations of intracellular trehalose can greatly improve the survival of mammalian cells during cryopreservation. Using a genetically engineered mutant of Staphylococcus aureus alpha-hemolysin to create pores in the cellular membrane, we were able to load trehalose into cells. Low concentrations (0.2 M) of trehalose permitted long-term post-thaw survival of more than 80% of 3T3 fibroblasts and 70% of human keratinocytes. These results indicate that simplified and widely applicable freezing protocols may be possible using sugars as intracellular cryoprotective additives.