Advertising: When the Big Guy Hits Back

For three years, Hertz Corp., the No. 1 company in the U.S. car-rental field, stood stolidly by while Avis Inc., No. 2, successfully needled away with its "We try harder" advertising campaign. But no longer. Now Hertz, having changed ad agencies, is trying to turn Avis' own theme against it. Typical of the new Hertz ads: "For years, Avis has been telling you Hertz is No. 1. Now we're going to tell you why."

Why did Hertz take so long to hit back? Carl Ally, 42, head of a four-year-old agency that bears...