Movie directors don’t commonly scope out automobile showrooms when looking for the stars of their next films. So when the director Michael Bay began poking around General Motors’s design studio in Los Angeles, GM executives knew they had a sterling marketing opportunity on their hands.

Mr. Bay directed “Transformers,” last summer’s blockbuster action movie based on the eponymous 1980s Hasbro toy line. Besides familiarizing a new generation of American boys with the age-old battle between the heroic Autobots and the dreaded Decepticons, the movie — and the subsequent release of the DVD and video game — left audiences lusting after the new GM models on which the robots’ disguises are based.

For anyone who didn’t come of age during the Reagan administration, an explanation of Transformers is probably in order. Briefly, they are mechanized alien beings that can morph into familiar, earthly gadgets. The good guys usually take the shape of cars and trucks. Their evil rivals tend to disguise themselves as weapons and helicopters straight out of the Cold War’s military-industrial complex.

Corporate America has used Hollywood to market its wares for decades. (Who can forget Reese’s Pieces, E.T.’s candy of choice?) But never before had a feature-length film — and a darn good one at that — stood as what is essentially a two-hour-long car commercial. “The cars are the celebrities in this film,” says General Motors’s director of branded entertainment and strategic alliances, Dino Bernacchi. “This was the greatest product placement of all time.” Before filming began, Mr. Bay got a glimpse of GM’s then-concept of a retrogressive Chevy Camaro. “The minute he laid eyes on it, he knew that the Camaro had to be Bumblebee,” says Mr. Bernacchi, referring to one of the most popular Autobot characters in the Transformers lineup.

The action movie begins with a Los Angeles-area dad buying his nerdy teenage son his first car: a beat-up, late-1970s Camaro. When the boy eventually learns that the car is indeed an alien life-form (Bumblebee the Autobot) disguised as his Camaro, he mocks the car’s shabby appearance.

Bumblebee then chooses to transform into a sleek, new 2008 Camaro, which, in real life, has yet to go on sale in showrooms. During test screenings before the movie’s release, audiences cheered each time Bumblebee turned into the new Chevrolet. “We knew we had one hot car on our hands,” Mr. Bernacchi says.

Mr. Bay also used the sexy Pontiac Solstice roadster and the tough-looking Hummer H2 as main characters in the film. Even better for GM was that one of the evil Decepticons disguises himself as a Ford Mustang police car.

Mr. Bernacchi grew up in suburban Michigan in what he calls a “non-car” family. He credits the 1977 Burt Reynolds flick “Smokey and the Bandit,” with its black Pontiac Firebird, as inspiring him to go into the car business.

Older colleagues of his have admitted to having similar experiences when first watching the classic Mustang chase scene in 1968’s “Bullitt,” starring Steve McQueen, or the many Sean Connery-era James Bond movies that spotlight the gunmetal-gray Aston Martin.

“These are examples of what’s called ‘organic integration,'” Mr. Bernacchi says. “You don’t have to push the product in other ways because it’s such an important and memorable part of the overall movie experience.”

One of the advantages the current “Transformers” movie has over memorable car flicks of the past is that it’s part of a larger product franchise. The DVD version of the film, which recently hit stores, has sold more than 8 million copies. Also in the mix are a video game, a comic book series, a run on HBO and network television, and, of course, a hotly anticipated sequel slated for 2009. Although Mr. Bay hasn’t approached GM yet to discuss which cars might star in the next “Transformers” installment, Mr. Bernacchi says he will be willing to lead another design-center tour when the time comes.