Allegations of insider trading always get the attention of lawyers. If they represent shareholders, they'll lick their chops. If they represent insiders, they'll start preparing a defense.

But lawyers aren't quite sure what to make of research indicating regulations intended to give executives some protection against insider trading allegations in certain circumstances may be having unintended consequences.

The research was done by Stanford University accounting professor Alan Jagolinzer, who looked at how executives fared when they sold company stock under so-called 10b5-1 plans.

The plans, named after a section of regulations adopted by the Securities and Exchange Commission in 2000, were designed to give executives more opportunities to sell shares as long as they didn't have inside information.

What Mr. Jagolinzer found when he looked at 3,400 insiders at 1,200 companies who disclosed stock sale plans between October 2000 and December 2005 indicates executives who used the plans did remarkably well for not having inside information.

Executives who used 10b5-1 plans beat the market by 6 percent over the subsequent six months while executives who didn't use them beat the market by only 1.9 percent, Mr. Jagolinzer found. Moreover, when executives terminated the stock sale plan before it ran its course -- something the SEC permits them to do -- the stock price subsequently rose a meaningful number of times.

Mr. Jagolinzer cautions it's not clear his findings indicate illegal behavior. But he says they suggest there might be more going on here than uninformed executives selling shares in order to diversify.

Given that another accounting professor, the University of Iowa's Erik Lie, tipped the SEC off to the stock options back-dating scandal, it's not surprising the agency has taken note of Mr. Jagolinzer's work.

"This raises the possibility that the plans are being abused in various ways to facilitate trading based on inside information," director of enforcement Linda Chatman Thomsen said in March. "We're looking at this hard."

Insider sales are always subject to scrutiny, particularly if the stock price subsequently heads south. That raises questions about whether the executive knew something bad was about to happen and sold before the bad news showed up in the stock price.

Because executives frequently have material, nonpublic information that could affect the stock price, companies impose strict restrictions on when they can sell.

The restrictions make it difficult for executives to sell for legitimate reasons such as diversifying their portfolios or paying for homes, college for their children or other major purchases.

Some executives "can almost never trade their shares," said attorney John G. Ferreira, who specializes in executive compensation issues for Morgan Lewis, Downtown. He says companies typically allow executives to buy or sell shares during the two or three weeks after quarterly earnings are released. After that, they'll more likely have nonpublic information about how the current quarter is going, information they can't use as the basis for buying or selling company stock.

The SEC tried to give executives a bigger window with 10b5-1 plans, which can be implemented when an executive doesn't possess inside information. The plans require executives to turn shares over to a third party who will sell a predetermined number over a predetermined period of time. As long as executives had no inside information when they initiated the plan, they have protection against insider trading charges.

The plans are quite common. Regional companies where executives are using them include Ampco-Pittsburgh, Universal Stainless & Alloy Products and Superior Well Services.

They also were used by two executives at New Century Financial, a subprime mortgage lender whose bankruptcy roiled financial markets this spring. The executives sold more than $22 million worth of New Century shares in the months before their company's troubles came to light.

Given Mr. Jagolinzer's findings and the SEC's tough talk, lawyers are advising corporate clients to review how their plans are being used. Their recommendations include not using the plans to sell large blocks of stock over a short period of time and to delay any stock sales until at least 30 days after a plan is implemented.

They're also telling clients not to end the plans prematurely even though SEC regulations allow them to -- even when they know something that other investors don't. Mr. Jagolinzer's discovery that a company's performance frequently improved after plans were terminated increases skepticism about an executive's motives for starting the sales in the first place. The skepticism is heightened if the executive subsequently implements a new plan.

"It certainly is something we generally advise executives not to do," Mr. Ferreira said.

Many observers expect the SEC will respond to Mr. Jagolinzer's findings by modifying the rules. Mr. Ferreira hopes that any changes won't handicap executives who have good reasons for selling.

"It's always popular to assume that executives are playing games," he said. "There are very legitimate reasons to let people use these plans."