Before the bell:

U.S. stocks were headed for a flat open Tuesday as investors took a step back from the previous session's rally. They also considered a more than 4% boost in Tokyo's Nikkei index as the nuclear situation in Japan continued to show signs of improvement.

U.S. stocks rallied for a third straight session Monday, as Japan made progress in cooling its nuclear reactors and investors cheered AT&T's (T) $39 billion deal to acquire T-Mobile.
The Dow finished Monday's session above the 12,000-point mark for the first time since the Japanese earthquake on March 11.
Oil for April delivery slipped 63 cents, or 0.6%, to $101.70 a barrel. May delivery will become the front-month contract after the close of trade, and it's already the most active contract, falling 62 cents, or 0.6%, to $102.47
World markets:

Economy: Investors don't have much to look at in the way of economic data Tuesday, with the Federal Housing Finance Agency's home price index the only report on deck.
Companies: After the close, software maker Adobe Systems (ADBE) and credit card company Discover (DIS) are on tap to report results.
Late Monday, news reports revealed that Apple had sued Amazon in California federal court. In the complaint, Apple asked a judge to block Amazon from using the term "Appstore." Three years ago, Apple was granted a trademark on its own "App Store."
Gold futures for April delivery fell $1.10, or 0.1%, to $1,425.30 an ounce.
The price on the benchmark 10-year U.S. Treasury was unchanged, holding the yield at 3.32%.