Populations of three isolates of Bursaphelenchus xylophilus, the pinewood nematode, and one of B. mucronatus were treated with three cryoprotectants at -70 C for 24 hours followed by deep freezing at -180 C in liquid nitrogen for different periods of time. A solution of 15% glycerol, 35% buffer S, and 50% M9, or 1% aqueous solution of dimethylsulfoxide (DMSO), or a mixture of 60% M9 and 40% S buffer were used as cryoprotectants. A significantly larger number of juveniles than adults survived deep freezing. Significantly more nematodes were motile after cryopreservation in the 15% glycerol-S-M9 soludon than in the M9-S buffer solution or the DMSO aqueous solution. When cryopreserved nematodes that had been treated with glycerol solution were plated onto Botrytis cinerea, they reproduced rapidly over several generations. Cryopreserved nematodes were as pathogenic as untreated nematodes to Scots pines.