The viability of the periodontal ligament (PDL) cells is critical for the successful healing of replanted exarticulated teeth. It is mainly dependent on the duration of the extra-alveolar time and the storage medium. Saliva has usually been recommended as the most suitable storage medium, but recent experimental studies indicate that milk is preferable. In the present study the effect on cultured PDL cells of saliva and milk has been compared with some reference media such as tap water or saline by means of a 3H-uridine leakage test. Storage in milk or saline was found to cause much less 3H-uridine leakage than storage in saliva or tap water. Cells stored in milk for 60-180 min showed about the same leakage as cells stored in saline or Hanks' balanced salt solution. Osmolality measurements showed that saliva was hypotonic, while the osmolality of milk ranged within physiological limits. When the osmolality of saliva was increased by addition of NaCl the leakage of the stored cells decreased to the level of cells stored in 0.9% NaCl or milk.