U.S. stock index futures were little changed on Friday as a bullish stock market was set to enter the seasonally weak month of May with the Dow and the Nasdaq about to post their best month since December.

Strong earnings, ample liquidity from the Federal Reserve, and the prospect of ultra-low interest rates for the rest of the year have driven stocks recently, pushing the Nasdaq to a 10-year high and the S&P 500 up over 8 percent this year.

There is a big bias toward the market going up and we've seen this through good news and what we would consider bad news. The market kind of shrugs it all off and keeps marching higher, said Kim Caughey Forrest, senior equity research analyst at Fort Pitt Capital Group in Pittsburgh.

I don't really understand what's driving it, but I guess you have to go with it, she said.

With an economy that grew less rapidly than hoped in the first quarter, investors will look to regional manufacturing data later Friday that could show an easing of activity.

Caterpillar Inc , the world's largest maker of heavy equipment, reported a fivefold surge in quarterly profit early Friday.

Chevron Corp is also scheduled to report results, with analysts expecting the second-largest U.S. oil company to show earnings per share of $3, against $2.36 a year ago.

S&P 500 futures rose 1.5 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 added 13 points, and Nasdaq 100 futures put on 1.5 points.

Shares of Research in Motion Ltd slumped 12 percent to $49.72 in premarket trading a day after the BlackBerry maker cut its first-quarter outlook, while Microsoft Corp dipped 1.7 percent to $26.25 after it recording a dip in quarterly sales of its core Windows operating system.

The dollar held near a three-year low against a basket of currencies and was on track for its biggest weekly fall since mid-January, with more losses possible due to end-of-the-month demand to sell dollars.

In other company news, Nasdaq OMX and IntercontinentalExchange were poised to go hostile in their bid for NYSE Euronext , sources said.

Samsung Electronics <005930.KS> filed a U.S. lawsuit against Apple Inc , accusing the iPad maker of infringing 10 patents in an escalation of the dispute over tablet and mobile technology.

(Editing by Jeffrey Benkoe)