- "This ain't a rescue mission, ape. You're on your own."
- ―Steve Haines
The Rhesus monkeys appear in the mission "Monkey Business" inside the Humane Labs and Research Facility. The monkeys are all in cages, and appear to be in a severely agitated state, possibly suffering from the effects of animal testing or due to the shootout. During the mission, at some point Haines will kick one of the cages, making a random comment before leaving. They can be shot by Michael.