NEW YORK — U.S. stocks climbed Monday, with the Standard & Poor’s 500 index posting a fifth quarterly gain, as Federal Reserve Chair Janet Yellen signaled continued monetary support and tensions appeared to ease in Ukraine.

NEW YORK — U.S. stocks climbed Monday, with the Standard & Poor’s 500 index posting a fifth quarterly gain, as Federal Reserve Chair Janet Yellen signaled continued monetary support and tensions appeared to ease in Ukraine.

Investors bought stocks that fell the most last week, with gauges of biotechnology and small-cap shares jumping at least 1.8 percent. Edwards Lifesciences rose 4.2 percent and Biogen Idec advanced 4 percent. Micron Technology surged 8 percent as the Nasdaq composite index rallied. Microsoft rose 1.7 percent after the chief executive officer named three top executives to lead some of the company’s businesses, adding to a series of management moves at the world’s largest software maker.

The S&P 500 rose 0.8 percent to 1,872.34. The gauge rose 0.7 percent in March to cap a 1.3 percent gain in the quarter, the longest streak since 2007. The Dow Jones industrial average rose 134.60 points, or 0.8 percent, to 16,457.66, sealing a second month of gains. The Nasdaq Composite index of technology stocks jumped 1 percent, erasing its loss for the year.

The S&P 500 fell 0.5 percent last week, as investors sold the bull market’s biggest winners to lock in gains as they assess how much of the recent economic weakness is weather- related and if the situation in Ukraine will worsen.

That trend reversed itself Monday, with the Russell 2000 index jumping 1.9 percent to erase a loss for the quarter after the gauge of small companies sank 3.5 percent last week. The measure capped a record seventh straight quarterly advance.

The Nasdaq Biotechnology index gained 3 percent, to trim its loss this month to 11 percent, the worst since May 2010. It plunged 7 percent last week after having rallied 79 percent in the 12 months through February.

"The main reason for the rally is the bounceback in the high flyers, which have been kicked in the teeth lately," Matt Maley, an equity strategist with Miller Tabak & Co., said in a phone interview from Boston. "Yellen’s comments were very positive, but the market was already up when she made them. It’s a combination of both."

Yellen said Monday "considerable slack" in the labor market is evidence that the central bank’s unprecedented accommodation will still be needed for "some time" to put Americans back to work.

"This extraordinary commitment is still needed and will be for some time, and I believe that view is widely shared by my fellow policy makers at the Fed," Yellen said.

She said March 19 that the central bank’s monthly bond purchases could end this fall and benchmark interest rates may rise about six months later. Fed Bank of Chicago President Charles Evans said March 28 that the central bank will probably increase interest rates in the second half of 2015.

Three rounds of central-bank bond purchases have helped the S&P 500 rally as much as 178 percent from its low in 2009.

"Yellen’s comments two weeks ago were taken with confusion, so she has an opportunity to calm things down today," Veronika Pechlaner, who helps oversee $2.3 billion as investment manager at Jersey, Channel Islands-based Ashburton, said by phone. "Initially, her comments were seen as rather hawkish but it’s become clear since then from other members that that wasn’t the intention."

The Institute for Supply Management-Chicago’s business barometer fell to 55.9 from 59.8 in February. Economists surveyed by Bloomberg expected a drop to 59.5.

Separate reports this week may show that manufacturing in the world’s largest economy expanded further this month, while factory orders probably rebounded in February, according to economists’ forecasts in Bloomberg News surveys. The government’s monthly jobs report is scheduled for April 4.

Russia and the United States agree on the need for a diplomatic solution to tensions over Ukraine, Russian Foreign Minister Sergei Lavrov said Sunday.

U.S. Secretary of State John Kerry said Russia must pull forces back from Ukraine’s border as both sides seek a diplomatic solution, while Lavrov urged the government in Kiev consider devolving power to give Ukraine’s regions more autonomy. The two top diplomats met Sunday in Paris.

"If there was any geopolitical risk, it’s calmed down and we’re showing some economic momentum," James Paulsen, chief investment strategist at Wells Capital Management, which manages about $360 billion, said by phone. "You take that combo package and say, do I really want to be short going into this jobs number? People are looking through the windshield and saying it looks like the economic data is going to pick up without weather distortion."

The Chicago Board Options Exchange volatility index, a gauge for U.S. stock volatility known as VIX, retreated 3.8 percent to 13.86, the lowest since Feb. 25. The index lost 1 percent in March. About 6.3 billion shares changed in on U.S. exchanges, 8.3 percent below the three-month average.

Nine of the 10 main S&P 500 groups advanced Monday. Materials, utilities and health-care stocks rose at least 1.1 percent to pace gains.

Edwards Lifesciences rose 4.2 percent to $74.17 and Medtronic climbed 1.9 percent to $61.54 after studies were released that will increase use of their man-made heart valves.

Amgen gained 2.3 percent to $123.34 after releasing data that showed its experimental heart drug was effective in lowering cholesterol.

Biogen Idec climbed 4 percent to $305.87 after its Alprolix drug to treat hemophilia B won approval from the Food and Drug Administration. The medicine may reduce the frequency of infusions required compared with current treatments, according to Executive Vice President Tony Kingsley.

Micron Technology rallied 8 percent to $23.66 to lead tech stocks higher. The S&P 500 gauge of technology companies dropped 1.1 percent last week.

Microsoft rose 1.7 percent to $40.99, the highest since July 2000. In an email to employees Monday, CEO Satya Nadella said he had appointed new leaders for the company’s cloud and enterprise organization, the Xbox business and the devices group. Nadella became CEO in February.

Netflix dropped 1.9 percent to $352.03, extending its loss this month to 21 percent, the worst since April 2012. The stock had rallied 137 percent in the 12 months through Feb. 28.

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With assistance from Bloomberg reporters Jeff Kearns in Washington and Namitha Jagadeesh in London.