* Yellen speech eyed for clues on interest rates
* Prana Biotech tumbles after Alzheimer's drug study results
* Chicago PMI on tap
* Futures up: Dow 81 pts, S&P 9.25 pts, Nasdaq 21.75 pts (Updates prices)
By Chuck Mikolajczak
NEW YORK, March 31 (Reuters) - U.S. stocks were poised to open higher on Monday, putting the S&P 500 on track for a second straight advance, ahead of a speech by Federal Reserve Chair Janet Yellen.
* Investors will peruse comments by Yellen, who is scheduled to speak in Chicago at 9:55 a.m. EST (1355 GMT), for clues on her stance on interest rates. On March 19, equities dropped after Yellen raised the possibility of an earlier-than-anticipated increase in rates.
* The S&P 500 is nearly flat for the month and up 0.5 percent for the quarter, on pace for the benchmark index's worst quarterly performance since the last quarter of 2012.
* Equities may get a boost on Monday from end of quarter "window dressing," when money managers adjust their positions to improve the look of their portfolios.
* S&P 500 e-mini futures rose 9.25 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures gained 81 points and Nasdaq 100 futures added 21.75 points.
* At 9:45 a.m. (1345 GMT), Chicago PMI data for March is due. Expectations are for a reading of 59 versus the previous reading of 59.8. Investors will continue to eye data for signs of improvement after lackluster data over the past several weeks was discounted as being linked to harsh winter weather.
* U.S.-listed shares of Prana Biotechnology Ltd tumbled 66 percent to $3.35 before the opening bell after the company said its experimental drug to treat Alzheimer's disease failed to meet the main goal of a mid-stage study in patients with a mild form of the condition.
* Many biotechnology stocks have come under pressure recently, and the Nasdaq Biotechnology index fell 7 percent last week, its fifth consecutive week of declines.
* Logistics company UTi Worldwide Inc reported a bigger-than-expected quarterly loss, hurt by weak demand for air freight as customers opted for cheaper modes of shipping.
* Investors continue to keep an eye on developments in Ukraine. U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov held talks on Sunday about ways to defuse the crisis while Prime Minister Dmitry Medvedev flaunted Russia's grip on Crimea on Monday by flying to the region and announcing plans to turn it into a special economic zone. (Editing by Bernadette Baum)