Republican presidential candidate Rudy Giuliani gained the endorsement Wednesday of a former GOP candidate — billionaire publisher and flat-tax proponent Steve Forbes.

Forbes ran for the White House in 1996 and 2000 as a Republican pushing a flat income tax rate.

The CEO of Forbes Inc., said Wednesday that Giuliani's record as mayor of New York City "showed how exercising fiscal discipline, including tax cuts, lowers deficits, spurs economic growth, and increases revenue."

Giuliani, a front-runner among Republicans seeking the White House in 2008, said he and Forbes share "an economic vision that embraces supply-side economics, tax relief, and spending restraint."

Back in 1996 when he was mayor, Giuliani dismissed Forbes' notion of a flat-tax as a "mistake," saying "the flat tax is not for me" because it would give states and cities more authority but less resources.

The pair also attended the opening bell ceremony at the NASDAQ stock exchange.