Wal-Mart's entry into health care may effect profound change by offering direct-to-consumer services and driving down prices for commodity services. Scott’s company is the master of this, and the health-care industry is, by and large, not used to competition. The basic-services segment is a less-demanding, low-end portion of the market not favored by the health-care giants. This plays well to Wal-Mart's strengths.

Wal-Mart, much like Apple, displays the key attributes of an XBD. And in just the way that Apple succeeded where Napster failed, Wal-Mart's size, brand appeal, strong finances, and resources should help it overcome resistance from hospitals, drug companies, and insurance providers. Given its legendary capability to innovate and execute, Wal-Mart may emerge as a superb XBD.

Judging from the comments of the business press and analysts, G.E. has a problem similar to Wal-Mart's: It’s too big. The company's market capitalization is $414 billion, and last year's revenue was $152 billion. Profits that inch up or down don’t seem to move the stock much. Something extraordinary is required.

What could be an opportunity worthy of the awesome resources held by one of the most aggressive corporations of our time? What could make G.E. into an XBD? In my email to Immelt, I suggested that he focus the company, or part of it, on developing an electric car.

A successful disrupter of the huge and complex energy industry has to be big, patient, and daring. I think G.E. has these qualities. Carmaker incumbents like General Motors, Ford, and Chrysler, as well as energy providers like Exxon Mobil, Royal Dutch Shell, and BP, seem reluctant to adapt to the needs of our economy, the environment, and our national security. It’s hard to think of a better fit than G.E.

G.E. Energy, which reported a profit of $3 billion on revenue of $18.8 billion in 2006, would likely benefit from a shift toward electric-powered transportation. It could tackle both an electric car and the construction of the infrastructure that electric vehicles would require. The use of electricity in transportation would allow us to exploit not only oil but also wind, hydro, nuclear, and photovoltaic energy, as well as coal and gas. This is a monumental change, and it is the only way our country can shed its dependence on foreign sources of energy.

I have no idea how much G.E. should spend on such an effort or how soon the behemoth could expect it to be profitable. But I do know that the needed funds are a match for G.E.’s vast balance sheet. Tesla Motors, a Silicon Valley startup, says it spent less than $105 million to develop its line of superfast electric vehicles. It's exciting that Tesla’s Roadster accelerates faster than most Porsches, but does the tiny carmaker have the resources to take on Detroit and the oil companies? G.E. does. Plus, the company’s name already reflects such a move.

I'm still waiting for Immelt to write back. And I’m wondering if he will. Maybe he’s already doing what he needs to and doesn’t want to give away G.E.’s secret. Scott hasn’t written back either. But Wal-Mart did hire Dr. John Agwunobi, the former assistant secretary for health at the U.S. Department of Health and Human Services, as senior V.P. to oversee the company’s health-care effort. And it continues to open more in-store clinics. Perhaps that’s Scott’s answer. If so, it's more eloquent than words.