Freeze tolerance and cryoprotectant synthesis was examined in Hyla regilla,
collected from Northern California in the spring and fall. Specimens froze
n at 2 C for six and 12 hours had a survival rate of 10% and 80%, respectiv
ely, in both seasons. This is the first report of freeze tolerance for H. r
egilla Freezing caused a fivefold increase in plasma glucose levels in the
spring and a 14-fold increase in the fall. Ice formation induced a rise in
liver glucose and glycerol production in both seasons with concentrations o
f liver glucose being greater in the fall than in the spring. The increase
in glucose was accompanied by a significant decline in liver glycogen. Seas
onal differences in muscle glycogen levels in response to freezing were not
shown, suggesting that the liver is the organ responsible for cryoprotecta
nt synthesis. The rise in plasma glucose, along with increased levels of li
ver glucose and glycerol in response to freezing; suggests that these compo
unds are being used as cryoprotectants, with glucose being the primary comp
onent.