If there's one lesson that the financial crisis of 2008 and 2009 taught us, it's that during the worst of times, cash is king. Companies that have cash have all the cards, as they can rest assured of being able to keep operating and even make purchases of promising acquisition targets. Those that don't have cash, on the other hand, have to rely on the credit markets to provide it -- and when those credit markets aren't functioning properly, cash shortages can bring those companies to the brink of collapse.

Last week, I looked at the companies in the Dow Jones Industrial Average (INDEX: ^DJI) that have the most cash on their balance sheets. This week, we'll turn to the other side of the spectrum and drill down on the Dow's cash-poor component stocks. First, though, let's look at how companies get into trouble with their cash.

The dangers of being cash-poor
As we saw last week, some businesses are just cash-generating machines. With minimal upfront costs to develop a product, profits just roll in once the product goes on sale. Those sales bring in more than enough cash flow to finance future research and development, pay overhead, and make interest payments to creditors and dividend payments to shareholders.

By contrast, though, other businesses require continual reinvestment of profits to maintain and upgrade existing production assets. Whether it's updating a production plant to meet new demand or finding the best employee talent to develop new blockbuster products, these companies often find themselves without much spare cash -- and often, substantial debt to boot.

Who's low on cash?
If you look only at cash and short-term investments on company balance sheets, two Dow companies stand out at the bottom of the list: Alcoa (NYSE: AA) and Caterpillar (NYSE: CAT), each of which has roughly $1.8 billion available. That's consistent with our theory about capital-intensive industries, as both companies are heavy-industrial manufacturers that require a lot of upfront capital to build plants and obtain the necessary raw materials to make their respective products.

But these companies are facing vastly different environments right now. Caterpillar has thrived on emerging-market growth, providing construction and mining equipment to growth-hungry regions of the world and pulling in immense profits in the process. Last week's announcement from China that GDP growth had slowed worried investors that the emerging-market boost might come to an abrupt end, but the company's prospects still look plenty bright for now.

On the other side of the coin, Alcoa has had to shutter production facilities in the wake of weak aluminum prices. Even though the company posted excellent results to begin the latest earnings season last week, CEO Klaus Kleinfeld said that Alcoa might end up taking even more production capacity offline in the months to come.

Both Alcoa and Caterpillar have far more long-term debt than cash on their balance sheets, leaving them both with between $6.5 billion and $7 billion in net debt. With low interest rates, financing that debt is no burden at the moment. But in time, it could pose a bigger threat to the companies if interest rates start to rise.

Who has big debts?
A low cash balance is a lot more dangerous when it's combined with huge amounts of debt. That's a situation that AT&T (NYSE: T) faces now, with $3.2 billion in cash versus more than $61 billion in long-term debt. The figures reflect the huge costs of building and maintaining the company's infrastructure, both for landlines as well as wireless networks. With technology advancing at an ever quicker pace, capital expenditures never seem to end, and while the company has more than $14 billion in free cash flow that it uses not only to carry its debt but also to pay a hefty dividend, there may come a time when obsolescence catches up with the carrier.

The same criticism applies to Verizon (NYSE: VZ) to a lesser degree. But with almost $14 billion in cash and short-term investments, Verizon has a much larger cushion against bad times. Moreover, with its joint venture with Vodafone on its wireless division, Verizon spreads the risk and has a partner to help cover some of those hefty capital expenses.

What to watch out for
With conditions as benign for cash-poor companies as you should ever expect to see, the risk they carry isn't obvious at the moment. Over the long haul, though, managing cash is an important aspect of running a business successfully. These companies aren't doomed, but they need to avoid becoming addicted to favorable credit terms before the low-rate punchbowl gets taken away for good.

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