Employees have learned certain truths about 401 plans.

What do you do with a plan distribution? Roll it into an IRA.But, heresy of heresies, sometimes it just ain't so.

If your plan is packed with your employer's stock - and if the shares have appreciated substantially - you may be better off not shifting them to an IRA.

Taking the stock means paying tax now, rather than later via the IRA route. But a special rule lets you pay tax on the value of the shares when you acquired them inside the plan, not on their current market value.

Appreciation - both inside the 401 before the distribution as well as in your non-IRA account afterward - is taxed only when you sell your shares and, at that point, qualifies as capital gains. You pay a maximum rate of 20 percent. Income from an IRA is taxed in your top tax bracket - up to 39.6 percent.

"With the long-running bull market and the drop in the capital-gains rate, this is a tremendous strategy," says Mark Cortazzo, a certified financial planner with the Macro Consulting Group, in Denville, N.J.

Well, it's a great strategy for some. The problem is it may be tough to figure out if you're one of the lucky ones.

If you need cash right away - to buy a business or a retirement home - keeping company stock out of a rollover probably makes sense since you'd be pulling the money out of the IRA soon and triggering the tax bill anyway.

If you don't expect to need the money during your lifetime, taking the stock also can be a real boon to your heirs. All appreciation from the time you took the stock out of the 401 to the time of your death becomes tax-free. If it were inside an IRA, it would be taxed in your beneficiary's top tax bracket.

You will have to pay tax on the dividends generated each year. And if you're under 55 when you cash out of the 401 taking the stock would subject you to a 10 percent penalty.

But as long as you take a lump-sum distribution from your retirement plan, you can roll over part of the company stock to an IRA and keep the rest on the outside.