The word ptyalism is of greek origin, and means "excessive secretion of saliva"1 or more commonly known as drooling.
Ptyalism may be seen in many circumstances, including both normal and serious conditions. Common causes of potentially serious ptyalism include: dental disease, oral foreign body or tumor, toxin or injury in the mouth, nausea, seizures, and liver or kidney disease, to name a few. Malformations of the jaws, teeth or muscles responsible for swallowing can also cause ptyalism. Common causes of "normal" ptyalism include extreme stress or nervousness and the hunger response to food.
If you notice your pet drooling beyond what is considered to be a normal response, please contact your veterinarian immediately -- it could be a sign of toxin ingestion or any number of potentially serious causes. Better to be safe now instead of sorry later.
Reference:
Ptyalism 1 Chicago Manual Style (CMS):
Ptyalism. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc.
http://dictionary.reference.com/browse/Ptyalism (accessed: April 11, 2008).

