Regan MacNeil: What an excellent day for an exorcism.
Father Damien Karras: You would like that?
Regan MacNeil: Intensely.
Father Damien Karras: But wouldn't that drive you out of Regan?
Regan MacNeil: It would bring us together.
Father Damien Karras: You and Regan?
Regan MacNeil: You and us.

Regan MacNeil: I'm not Regan.
Father Damien Karras: Well, then let's introduce ourselves. I'm Damien Karras.
Regan MacNeil: And I'm the Devil! Now kindly undo these straps!
Father Damien Karras: If you're the Devil, why don't you make the straps disappear?
Regan MacNeil: That's much too vulgar a display of power, Karras!

Regan MacNeil: Your mother's in here, Karras. Would you like to leave a message? I'll see that she gets it!

Regan MacNeil: Your mother sucks cocks in Hell, Karras!

Father Merrin: The demon is a liar. He will lie to confuse us. But he will also mix lies with the truth to attack us. The attack is psychological, but powerful. So don't listen, remember that, do not listen.

Regan MacNeil: You can bring Mr. Dennings if you like...Well, you like him...You're gonna marry him, aren't you?
Chris MacNeil: Oh God, are you kidding me? Marry Burke Dennings! Don't be silly. Of course not. Where'd you ever get an idea like that?
Regan MacNeil: But ya like him.
Chris MacNeil: Of course I like him. I like pizzas too, but I'm not gonna marry one.
Regan MacNeil: You don't like him like Daddy?
Chris MacNeil: Regan. I love your Daddy. I'll always love your Daddy, honey. OK? Burke just comes around here a lot, 'cause, well, he's lonely. Don't got nuttin' to do.
Regan MacNeil: [Coy] Well, I heard differently.
Chris MacNeil: Oh you did. What did you hear? Huh?
Regan MacNeil: I don't know. I just thought.
Chris MacNeil: Well, you didn't think so good.
Regan MacNeil: How do you know?
Chris MacNeil: 'Cause Burke and I are just friends. OK? Really. OK.

Father Damien Karras: It's my mother, Tom. She's alone. I never should have left her. At least in New York, I'd be near, I'd be closer.
Tom: Could see about a transfer, Damien.
Father Damien Karras: I need re-assignment, Tom. I want out of this job. It's wrong. It's no good.
Tom: You're the best we've got.
Father Damien Karras: Yeah, not really. It's more than psychiatry, and you know that Tom. Some of their problems come down to faith, their vocation and meaning of their lives, and I can't cut it anymore. I need out. I'm unfit. I think I've lost my faith, Tom.

Dr. Klein: Pathological states can induce abnormal strength. Accelerated motor performance. Now, for example, say a 90 pound woman sees her child pinned under the wheel of a truck. Runs out and lifts the wheels a half a foot up off the ground -- you've heard the story -- same thing here. Same principle, I mean.
Chris MacNeil: So what's wrong with her?
Dr. Klein: We still think the temporal lobe.
Chris MacNeil: Oh what are you talking about, for Chrissakes?! Did you see her or not? She's acting like she's fucking out of her mind, psychotic, like a... split personality or ...
Dr. Klein: There haven't been more than a hundred authentic cases of so-called split personality, Mrs. MacNeil. Now I know the temptation is to leap to psychiatry. But any reasonable psychiatrist would exhaust the somatic possibilities first.
Chris MacNeil: So, what's next?
Dr. Klein: A pneumoencephalogram, I would think. Pin down that lesion. It will involve another spinal.
Chris MacNeil: Oh, Christ!
Dr. Klein: What we missed in the EEG and the arteriograms could conceivably turn up there. At least, it would eliminate certain other possibilities.

Psychiatrist: Is there someone inside you?
Regan MacNeil: Sometimes.
Psychiatrist: Who is it?
Regan MacNeil: I don't know.
Psychiatrist: Is it Captain Howdy?
Regan MacNeil: I don't know.
Psychiatrist: If I ask him to tell me, will you let him answer?
Regan MacNeil: No!
Psychiatrist: Why not?
Regan MacNeil: I'm afraid.

Dr. Klein: There is one outside chance for a cure. I think of it as shock treatment -- as I said, it's a very outside chance... Have you ever heard of exorcism? Well, it's a stylized ritual in which the rabbi or the priest try to drive out the so-called invading spirit. It's been pretty much discarded these days except by the Catholics who keep it in the closet as a sort of an embarrassment, but uh, it has worked. In fact, although not for the reasons they think, of course. It's purely a force of suggestion. The victim's belief in possession is what helped cause it, so in that same way, a belief in the power of exorcism can make it disappear.
Chris MacNeil: You're telling me that I should take my daughter to a witch doctor? Is that it?

[Regan, possessed, is masturbating herself with a crucifix.]
Regan MacNeil: Let Jesus fuck you, let Jesus fuck you! Let him fuck you!

Chris MacNeil: You show me Regan's double, same face, same voice, everything. And I'd know it wasn't Regan. I'd know in my gut. Now, I want you to tell me that you know for a fact that there's nothing wrong with my daughter, except in her mind. YOU TELL ME FOR A FACT YOU KNOW AN EXORCISIM WOULDN'T DO ANY GOOD! YOU TELL ME THAT!

Father Damien Karras: I think it might be helpful if I gave you some background on the different personalities Regan has manifested. So far, I'd say there seem to be three. She's convinced...
Father Merrin: There is only one.

Father Damien Karras: Take me! Come into me! God damn you! Take me! Take me!