You can change another's behavior with a successful check. Your Intimidate check is opposed by the target's modified level check (1d20 + character level or Hit Dice + target's Wisdom bonus [if any] + target's modifiers on saves against fear). If you beat your target's check result, you may treat the target as friendly, but only for the purpose of actions taken while it remains intimidated. (That is, the target retains its normal attitude, but will chat, advise, offer limited help, or advocate on your behalf while intimidated. See the Diplomacy skill, above, for additional details.) The effect lasts as long as the target remains in your presence, and for 1d6x10 minutes afterward. After this time, the target's default attitude toward you shifts to unfriendly (or, if normally unfriendly, to hostile).
If you fail the check by 5 or more, the target provides you with incorrect or useless information, or otherwise frustrates your efforts.
Demoralize Opponent: You can also use Intimidate to weaken an opponent's resolve in combat. To do so, make an Intimidate check opposed by the target's modified level check (see above). If you win, the target becomes shaken for 1 round. A shaken character takes a -2 penalty on attack rolls, ability checks, and saving throws. You can intimidate only an opponent that you threaten in melee combat and that can see you.
Action: Varies. Changing another's behavior requires 1 minute of interaction. Intimidating an opponent in combat is a standard action.
Try Again: Optional, but not recommended because retries usually do not work. Even if the initial check succeeds, the other character can be intimidated only so far, and a retry doesn't help. If the initial check fails, the other character has probably become more firmly resolved to resist the intimidator, and a retry is futile.
Special: You gain a +4 bonus on your Intimidate check for every size category that you are larger than your target. Conversely, you take a -4 penalty on your Intimidate check for every size category that you are smaller than your target.
A character immune to fear can't be intimidated, nor can nonintelligent creatures.
If you have the Persuasive feat, you get a +2 bonus on Intimidate checks.
Synergy: If you have 5 or more ranks in Bluff, you get a +2 bonus on Intimidate checks.
The DC to intimidate any creature whose attitude is fanatic is increased by +20.
Source: SRD 3.5 Combined Skills