DETROIT —  General Motors Corp. (GM) and Toyota Motor Co. (TM), the world's two largest automakers, said Thursday they will extend a collaborative research agreement for another two years.

The two automakers will focus on safety and energy research. They will look at vehicle-to-vehicle communications systems and other technology that can help prevent crashes as well as ways to cut down on vehicle emissions, GM spokesman Scott Fosgard said.

GM and Toyota first began working with each other on hybrid vehicles and hydrogen fuel cells in 1999. They extended that agreement in 2004 but dropped hybrid technology to concentrate on fuel cells. The latest agreement, which would have expired at the end of this month, will now be extended to March 31, 2008.

Fosgard said the companies are no longer collaborating on fuel cells because that technology is moving out of the research stage and into the more proprietary development stage. But Fosgard said both companies remain open to other research projects in mutually beneficial areas.

GM shares fell 29 cents, or 1.5 percent, to $19.61 in afternoon trading on the New York Stock Exchange, while Toyota's U.S. shares slipped 32 cents to $106.72.

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