As the Dow Jones industrial average was plunging 311 points on Thursday, Richard Riggs was working and unworried.

The owner of a small collection agency in Los Angeles, Riggs, 52, says he has about 25 per cent of his assets in stocks - an amount that won't make or break him.

"Confidence in your basic strategy is everything," he said. "We live within our means, drive paid-off cars and travel well. We are content and unafraid."

What to do when the market goes mad? Financial planners say people should invest for the long haul and not be panicked by short-term swings. But they also advise regular checkups to ensure your portfolio is healthy.

Here are some questions to ask as you review your investments.

What's your overall mix?

Just as a smart diet includes a mixture of food groups, a healthy portfolio requires a mixture of different assets. Every portfolio ought to include a mix of stocks, bonds, cash and international investments, said Ed O'Hara, a financial planner from Silver Spring, Maryland.

The right percentage of each will depend on factors including your age, wealth and ability to tolerate risk.

The younger and more risk tolerant, the more you can handle a larger percentage of stocks.

What does your close-up look like?

Breaking investments into broad asset categories is just the first step in diversifying a portfolio, said Brent Kessel, chief executive of Kubera Portfolios in Los Angeles.

You need to look closely at your specific investments, especially your stocks, to make sure you are not too heavily weighted in one sector, such as technology or financial services.

In other words, it is not enough to just eat vegetables - you need dark greens, orange carrots, yellow corn and other varieties to ensure a balanced diet.

There are many ways to diversify within a stock portfolio. Some experts suggest that you have investments in a wide array of market sectors.

When was your last check-up?

Even if you have different asset classes and a wide array of investments in each class, you need to make sure that the percentage of assets that you have in each category remains consistent with your plan, said Mark Brown, principal with the Denver financial planning firm of Brown and Tedstrom.

Investors who are just a few years from retirement, for example, might decide that they want 60 per cent of their assets in stocks, 30 per cent in bonds and 10 per cent in cash.

But, when one market soars, or plunges, those percentages are likely to get out of balance.

Unfortunately, when times are good, investors get complacent and forget their periodic portfolio check-ups. If you haven't looked lately at whether your asset mix suits your plan, do it now.

How are your fundamentals?

If you invest in individual stocks, it might be time to take a look at whether you would buy the same shares today, Brown added.

That means taking a look at fundamentals, such as the company's stock price compared to its earnings; its growth prospects and its dividend yield. Are these ratios in line with historic levels for this company and this industry? If not, is there some fundamental reason why they should be off-kilter?

If a company's market price is high compared to its earnings - both relative to its historic P/E and to its peers - it may be time to sell.