GameSpot has published an extensive three-page interview with Irrational Games' Ken Levine about their upcoming RPG hybrid, BioShock.
Q: Tell us about the substance adam and how it works in the game. Will it act as a kind of currency? Will it always be in short supply?
A: In the game, adam is the underlying currency that drives everything in Rapture, because it powers all the genetic mutations. It's the genetic fuel of the world, essentially.
There's lots of ways to get adam. The primary way is through the gatherers, because the only way that adam can be reused is when it's recycled through the bodies of the little sisters. So, they're essentially like little armored cars, carrying around the world's most precious resource, protected by the big daddies.
You use adam essentially like money, to buy everything. You use it in vending machines, when you hack security systems (it costs adam for that interaction)--it's everywhere in the world. According to our story, adam comes from an extinct sea slug. So, there are no more new sources of adam--the only way to get more adam is to recycle it from dead bodies. And that's what these little sisters do. But [the citizens of Rapture] ended up killing all the sea slugs in the process of all the troubles they had down there.