Rats require significant amounts of exercise each day. In addition to allowing plenty of space within the cage, plan on giving each rat at least an hour of supervised play outside the cage. Bored, underexercised rats are not pleasant companions! Think about it: would you keep a human toddler in a playpen all day, every day?

Rats have a reputation for not using exercise wheels. That reluctance has less to do with the exercise preferences of the rats than it does with the design of most conventional wheels, which can hurt their feet and injure their tails. Most rats will use a correctly designed wheel, and reputedly those who do so regularly experience a slower mental decline in old age than rats that don't. My rats love their 12" Wodent Wheel "Wobust", which not only is correctly sized and shaped to prevent injury, but also features a design that makes them feel like they're in an enclosed space. The only other wheel I know of rats using is a 12" Silent Spinner. Don't waste your money on smaller wheels, even for younger rats, or you'll witness scenes like Eve napping in the picture to your right! Rats also love running through tunnels, so be sure to check out ferret tunnels, or make your own with PVC pipe. 

I've also had great success with walking rats on harnesses with leashes. Opinions as to the best harness varies with both the owner and the rat. I really like the comfort harnesses with velcro straps, but my rats were universally terrified of the sound made by the velcro. The very simple all in one figure 8  harness sold by Coastal for rabbits has been accepted by almost all of mine. Just remember that in most cases, you should plan to follow the rat and use the leash only to keep it out of trouble, rather than lead the rat like a dog. Still, one of mine heels better than any dog I've ever owned!