The S&P 500 scored its fourth straight day of gains.

Actavis Plc, Gilead Sciences and other biotechs were among the biggest drivers, a day after Allergan agreed to be bought by Actavis. The Nasdaq biotech index rose 2.1 percent.

The S&P health care index added 1.6 percent. Shares of Actavis were up 8.7 percent at $269.60, helped by bullish analyst notes, while Gilead's stock rose 3.3 percent to $103.71 percent.

"A little bit of a risk trade is coming back on, and those are the areas for the M&A," said Uri Landesman, president of Platinum Partners in New York. "It's a very, very good environment to buy growth, so I don't quibble with the notion that there's going to be more M&A."

Among the biggest boosts to the Dow, shares of UnitedHealth were up 1.8 percent at $98.19.

Further supporting stocks, news of a snap election and a delayed tax increase in Japan strengthened hopes for new stimulus, a day after data showed Japan back in recession. In Europe, German analyst and investor sentiment advanced this month for the first time in almost a year.

Benign U.S. inflation data also helped.

The Dow Jones industrial average rose 40.07 points, or 0.23 percent, to 17,687.82, a record high. The S&P 500 gained 10.48 points, or 0.51 percent, to 2,051.8, its biggest one-day move since Nov. 5.

The Nasdaq Composite added 31.44 points, or 0.67 percent, to 4,702.44.

Actavis Gains

Actavis was the S&P's biggest percentage gainer; the largest decliner was Urban Outfitters, down 6.6 percent at $28.79, following results.

On the Nasdaq 100, the largest gainer was Dish Network , up 3.9 percent to $67.85, while the largest decliner was Staples, down 1.6 percent at $12.76.

Among the most active NYSE stocks were Petrobras, up 0.96 percent at $9.42, and General Electric, up 1.50 percent at $27.01. On the Nasdaq, Apple, up 1.3 percent to $115.47, was among the most active.

About 6.1 billion shares traded on U.S. exchanges, below the 6.4 billion average this month, according to BATS Global Markets.

NYSE advancers outnumbered decliners 1,862 to 1,217, for a 1.53-to-1 ratio; on the Nasdaq, 1,645 issues rose and 1,079 fell for a 1.52-to-1 ratio.

The S&P 500 posted 77 new 52-week highs and one new low; the Nasdaq Composite recorded 95 new highs and 56 new lows.