How big is financing in the economy? One way tomeasure it: 18% of the $13 trillion market value of S&P 500companies is for the financial sector. That bulge is a big part of whythe market has been choppy since last summer: Credit problems aredragging down the banks, brokers and insurers. Another measure isprofits. The finance sector accounts for 28% of the index's combined$748 billion in earnings for 2006. Those earnings are likely to be downin 2007 when writeoffs are included. Neither of these percentages forfinancial services includes the financial activities of companies likeSony and GE.

Here's another way to look at how much is riding onthe soundness of borrowers. Debt at U.S. households, governments (stateand federal) and nonfinancial businesses now stands at 217% of grossdomestic product, up from 141% a quarter of a century ago. So a smallrise in interest rates or in defaults is likely to have a bigger impactthan it once would have had on business bottom lines and consumers'ability to spend.

"The debt level is unprecedented, and theacceleration in the growth of the debt hasn't been seen since the1920s," says Christopher Watling of Longview Economics in London. "Lotsof businesses have profited off this, and they're vulnerable."

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