The tolerance of freezing and associated accumulation of cryoprotectants was studied in an Arctic population of the enchytraeid Fredericia ratzeli. At -3 and -5 degrees C specimens readily froze when slowly cooled in contact with moist soil. A small fraction of the animals (10-20 %) survived internal ice formation under these circumstances. Frozen specimens had elevated glucose concentrations as compared to unfrozen control animals acclimated at 0 degrees C. In a fraction of the animals, equal to the fraction surviving freezing, a high concentration of glucose was detected. The highest values amounted to ca. 150 microg mg(-1) dry weight, corresponding to ca. 270 mmoles L(-1). It is argued that the physiology of freeze tolerance in this enchytraeid resembles the physiology described for freeze tolerant earthworms and frogs.