David Tennant (The Doctor) and Mark Gatiss (Professor Lazarus) previously appeared in the 2003 Big Finish Doctor Who Unbound audio drama Sympathy for the Devil together. They played Colonel Brimmicombe-Wood and the Master respectively. This production featured David Warner as the Doctor.

Lazarus: That's an interesting perfume. What's it called?
Tish: (clearly disgusted) Soap.

The Doctor: Oh look, they’ve got nibbles! I love nibbles!

Tish: (referring to the Doctor) He's a science geek, I should've known. Gotta get back to work now, I'll catch up with you.
(Tish leaves)
The Doctor: Science geek, what's that mean?
Martha: That you're obsessively enthusiastic about it.
The Doctor: (pleased) Oh, nice.

The Doctor: Lovely to meet you, Mrs. Jones. I've heard a lot about you.
Francine: (coldly) Have you. What have you heard, then?
The Doctor: Oh, y'know, that you're Martha's mother, and...Uhm...no, actually, that's about it. We haven't had much time to chat. You know, been... busy.
Francine: "Busy?" Doing what, exactly?
The Doctor: Oh, y'know...stuff.

Lazarus: I am Professor Richard Lazarus. And tonight, I'm going to perform a miracle...

Martha: It’s impossible.
The Doctor: And that’s two impossible things we’ve seen so far tonight. Don’t you love it when that happens?

Martha: (referring to Lazarus) Tish, he's a monster!
Tish: I know the age thing's a bit freaky but it works for Catherine Zeta-Jones!

Martha: You mean you don’t have a plan?
The Doctor: Yes, the plan was to get inside here. Well, then I’d come up with another plan.
Martha: In your own time, then.

The Doctor: Really shouldn't take that long just to reverse the polarity...Must be a bit out of practice.

The Doctor: Lazarus, back from the dead...Should've known, really.

(The Doctor and Lazarus are in Southwark Cathedral)
Lazarus: Came here before. A lifetime ago. Thought I was going to die then. In fact, I was sure of it. I sat here, just a child, the sound of planes and bombs outside.
The Doctor: The Blitz.
Lazarus: You've read about it.
The Doctor: I was there.
Lazarus: You're too young.
The Doctor: So are you.

Lazarus: I changed the course of history.
The Doctor: Any of them might have done too. You think history's only made with equations? Facing death is part of being human. You can't change that.
Lazarus: No, Doctor. Avoiding death is being human. It’s our strongest impulse. To cling to life with every fibre of being. I’m only doing what everyone before me has tried to do. I’ve simply been more... successful. I'm more now than I was. More than just an ordinary human.
The Doctor: There's no such thing as an "ordinary human."
Lazarus: You're so sentimental, Doctor. Maybe you are older than you look.
The Doctor: I'm old enough to know that a longer life isn't always a better one. In the end, you just get tired. Tired of the struggle. Tired of losing everyone that matters to you. Tired of watching everything turn to dust. If you live long enough, Lazarus, the only certainty left is that you'll end up alone.
Lazarus: That's a price worth paying.
The Doctor: Is it?

Francine: (over the phone) Martha, it's your mother. Please, phone me back, I'm begging you! I know who this Doctor really is! I know he's dangerous! You're going to get yourself killed! Please trust me! This information comes from Harold Saxon himself. You're not safe!

Harold Saxon

This is possibly a reference to Harold Godwinson, the last Anglo-Saxon King of England from January 5 to October 14, 1066.

This episode reveals that Mr. Saxon's first name is Harold.