Reports that retailers Office Depot and OfficeMax are discussing a combination come shortly after several big corporate deals were announced in recent weeks. Both stocks were up sharply in early trading.
The Standard & Poor's 500 index rose three to 1,523. The Nasdaq composite also rose three points to 3,195.
Markets were higher in Europe following news that the German economy is picking up steam. Indexes rose about 1 percent in Germany, France and Britain.
Asian markets were mostly down because of concerns about Chinese real estate curbs.
Tuesday's runup follows a bullish trend in recent days.
Traders returned to their desk following a three-day holiday weekend in an optimistic frame of mind Monday , with the Dow Jones industrial average 0.4 percent higher at 14,032, around 130 points shy of its record close set in October 2007. The broader S&P 500 index rose 0.2 percent to 1,523.