Horseradish hairy root cultures were successfully cryopreserved by encapsulation-dehydration. Roof tips excised from the cultures were encapsulated in Ca-alginate beads containing 0.5 M glycerol and 0.3 M sucrose, and then the beads were slowly dehydrated by air-drying over silica gel to reduce the water content to 33% prior to cooling in liquid nitrogen. Preculture and dehydration of the root tips in the presence of 2 mu M abscisic acid was effective in increasing the survival rate, regeneration of hairy roots being observed in about 60% of the tips dehydrated and cooled in liquid nitrogen.