Shares of AtheroGenics ( AGIX) dropped Tuesday after the company said it would issue clinical trial results on a heart disease drug by the end of the first quarter, a later date than investors wanted to see.

The stock had soared 24% on Friday as speculation mounted that AtheroGenics would deliver long-awaited news about the drug AGI-1067 this week at a biotechnology conference in San Francisco.

The volatility illustrates a common problem in biotech stocks -- they can rise quickly on speculation and fall just as quickly on reality. As trading wound down, the stock was sliding $1.19, or 9.6%, to $11.27 on volume that was triple the daily average. The stock fell as low as $10.57.

AtheroGenics had been telling investors that it expected clinical trial data to be revealed early in 2007. On Monday night, the company said it "further refined" its guidance, adding that it wants to have the results ready for the American College of Cardiology's annual scientific meeting in late March.

AGI-1067 is attracting attention from investors because the drug is the Alpharetta, Ga.-based company's most advanced product. There's big money at stake thanks to a December 2005 deal with AstraZeneca ( AZN) that could provide AtheroGenics with as much as $1 billion, excluding sales-based royalties, if the product comes to market.

Investors in AstraZeneca are paying close attention, too, because the Anglo-Swedish drugmaker badly needs a new hit product. In recent years, it has suffered a string of expensive failures -- via its own research or a partner's R&D -- involving experimental treatments for diabetes, stroke and preventing blood clots. AstraZeneca's stock was off 14 cents to $54.28.

AGI-1067 is being developed as a way to reduce plaque that blocks arteries and can lead to a heart attack or stroke. Rather than fight cholesterol, AGI-1067 blocks an inflammation process that leads to atherosclerosis, or the buildup of plaque in the arteries.

The drug affects certain cells in the inner lining of blood vessels, disrupting a process that creates proteins that cause inflammation. AtheroGenics says this inflammation leads to atherosclerosis.