AFI #077 Charlton Heston as Det. Robert Thorn from Soylent Green (1973)

Det. Thorn: Hatcher, get to the Exchange. You gotta tell them they're right.
Hatcher: But let's take care of you first.
Det. Thorn: You don't understand. I've got proof. They need proof, I've seen it. I've seen it happening. They've gotta tell people.
Hatcher: Tell them what?
Det. Thorn: The ocean's dying. Plankton's dying. It's people. Soylent Green is made out of people. They're making our food out of people. Next thing, they'll be breeding us like cattle for food. You've gotta tell them. You've gotta tell them!
Hatcher: I promise. Tiger. I promise. I'll tell the Exchange.
Det. Thorn: You tell everybody. Listen to me. Hatcher. You've gotta tell 'em! SOYLENT GREEN IS PEOPLE! We gotta stop them! Somehow! Listen! Listen to me… PLEASE!!!

- Charlton Heston as Det. Robert Thorn from Soylent Green (1973)

The bolded line is ranked #77 in the American Film Institute's list of the top 100 movie quotations in American cinema.