From Rules Cyclopedia:
Morale (Optional)
DMs are free to ignore this rule entirely, and they can gauge the morale based on the situation, the nature of the creature involved, and any other factors they deem as relevant. The morale check is supposed to be a convenience for the DM, to give him a quick way to decide how creatures react; it's not a straight-jacket to keep him from role-playing a character the way he sees that character behaving.
DM rolls 2d6 against creature's morale score (found in monster descriptions). If 2d6 roll is equal to or less than morale score, creature pursues combat; otherwise, it avoids combat. Only NPCs and monsters roll morale; PCs make their own decisions.