They have run all the way from Devonport, Tasmania in the name of children's cancer research.

The Tasmanian pair has crossed Bass Straight and already run more than 500 kilometres over four days, but the duo still has another 500 kilometres to go before reaching Bondi Beach.

Tim and Shane are hoping to raise $100,000 to be split between charity groups the Tim Blair Run for Kids Foundation and the Kids Cancer Project.

"I'm a firm believer in that our biggest responsibility is the kids," Tim said.

"No kid has asked for cancer."

Tim and Shane were visibly exhausted yesterday as they stopped for a break on the side of the road with their support team.

Sitting in a car applying an ice pack to a stress fracture in his lower left leg, Tim said it was "onward and upward" for the remainder of the run and its cause.

"I've been crook and that's always a pretty big reality check," he said.

"I've known four people that have passed away from cancer - it doesn't discriminate.

The duo arrived in Gundagai on Monday night before departing for Yass on Tuesday.

The final leg of their run sees them arrive at Bondi on Sunday.

"The people that donate are the real heroes. They are the ones that make a difference," Tim said.