Results from the survey of 146 investors were released late on Tuesday by Mark Schoenebaum, a pharmaceutical analyst for the investment research services group. Wall Street is eagerly awaiting results of the trials and expects huge potential sales if either of the medicines proves able to arrest the progression of the memory-robbing disease.

Pfizer and Lilly are expected in the third quarter to disclose the main findings from large studies of their respective medicines, bapineuzumab and solanezumab. Complete data are expected to be presented at medical meetings in the fourth quarter.

The survey responders, on average, gave solanezumab only a 14 percent chance of meeting all the primary goals of its two Phase III studies, compared with an average 21 percent probability for the two big trials of bapineuzumab, Schoenebaum said.

Likewise, responders cite an average 15 percent probability of the Lilly's drug winning approval from the U.S. Food and Drug Administration sometime in the next two years, compared with 29 percent odds for bapineuzumab.

Lilly only tested solanezumab in 12-week mid-stage trials before moving it into large Phase III studies. By contrast, Pfizer's mid-stage trials of bapineuzumab lasted 18 months, better enabling Pfizer to pick appropriate doses of its medicine for the far larger Phase III studies.

That potential advantage for the Pfizer drug might account for some of the greater confidence in bapineuzumab.

Lilly desperately needs revenue from big-selling new drugs to offset plunging sales of its Zyprexa schizophrenia medicine, now facing cheaper generics and the approaching collapse of other top Lilly drugs that will confront generics.

Solanezumab would be just the ticket and some analysts have forecast that Lilly shares could jump 50 percent, or even double, if the injectable drug proves safe and effective in the trials and is approved. Pfizer, which is rebounding from years of anemic sales and earnings thanks to cost controls and new medicines, could also be transformed if its Alzheimer's drug goes the distance.

Should solanezumab fail to show any signs of effectiveness, however, Lilly shares would likely drop to about $37.40, according to the average estimate in Schoenebaum's survey. That would represent a decline of almost 12 percent from Lilly's closing share price on Tuesday of $42.29.

Pfizer shares, in the event its drug completely fails, would likely fall to about $21.30, responders said, representing about a 6 percent decline from their current price.

Alzheimer's disease affects an estimate 5 million Americans and more than 35 million people worldwide and its incidence is increasing with the aging population.

(Reporting By Ransdell Pierson in New York; editing by Andre Grenon)

• A Permanent Economic Emergency