The U.S. stock market capped a four-day losing streak with its biggest drop of the week.
Disappointing quarterly results and outlooks from several companies pulled the major stock indexes sharply lower on Friday. New signs pointing to a slowing of China's economy also added to investor jitters, bringing down the price of oil and other commodities.
While corporate profits have mostly exceeded Wall Street's expectations so far this earnings season, investors have grown uneasy as many companies provided cautious outlooks or weak sales.
"The revenue numbers have been very shaky," said JJ Kinahan, TD Ameritrade's chief strategist. "After next week, we'll have a much better picture overall how the earnings season was. But right now, that's the theme that I'm seeing, and it's not a healthy one."
The mixed company earnings increasingly weighed on stocks as the week wore on. The Standard & Poor's 500 index has now lost ground four out of the last five weeks.
The S&P 500 ended the day down 22.50 points, or 1.1 percent, to 2,079.65, while the Dow Jones industrial average slid 163.39 points, or 0.9 percent, to 17,568.53. The Nasdaq composite lost 57.78 points, or 1.1 percent, to 5,088.63.
Stocks kicked off the week on a strong note, driving the Nasdaq to its latest record high and bringing the S&P 500 close to a milestone of its own. But it's been downhill since then. The Dow fell into negative territory for the year on Thursday. As of Friday, it was down 1.4 percent for 2015.
The tech-focused Nasdaq remains the best-performing index for the year. It's up 7.4 percent, compared with 1 percent for the S&P 500.
Trading got off to an uneven start on Friday. The major indexes were all down by midmorning as traders sized up the latest corporate earnings.
Biotechnology company Biogen and pharmaceutical company AbbVie both reported a better-than-expected second-quarter profits, but their revenue fell short of Wall Street forecasts. Biogen plunged $85.02, or 22.1 percent, to $300.03. AbbVie declined $2.44, or 3.5 percent, to $68.08.
Capital One Financial, which announced quarterly results a day earlier that failed to live up to financial analysts' expectations, sank 13.1 percent. The stock ended down $11.91 at $78.86.
Even a dash of merger news, which often puts investors in a buying mood, failed to impress.
Anthem agreed to buy rival Cigna for $48 billion in a deal that would create the nation's largest health insurer by enrollment, covering about 53 million U.S patients. Anthem fell $4.35, or 2.8 percent, to $150.86, while Cigna lost $8.64, or 5.6 percent, to $145.72.
Investors did welcome Amazon's latest quarterly report card. The e-commerce pioneer announced a surprise profit late Thursday. The stock vaulted $47.24, or 9.8 percent, to $529.42.
Nine of the 10 sectors in the S&P 500 ended lower. Health care stocks fell the most, 2.5 percent. Utilities edged higher.
Of the 187 companies in the S&P 500 that have reported earnings so far, about 72 percent of them have delivered results that beat Wall Street estimates, according to S&P Capital IQ. That's better than the historical average of 66 percent.
"Generally most companies are seeing modest growth, but nothing to write home about," said Brad Sorensen, managing director of market and sector analysis at Schwab Center for Financial Research.
Another 163 companies, or a third of the S&P 500, are due to report earnings next week, including Facebook, Twitter and Exxon Mobil.
In energy trading, the price of oil continued to slide Friday as the number of rigs drilling for oil in the U.S. rose. Benchmark U.S. crude fell 31 cents to close at $48.14 a barrel in New York. Crude fell 5 percent for the week, and is down 19 percent for the month. Brent crude, a benchmark for international oils used by many U.S. refineries, fell 65 cents Friday to close at $54.62 a barrel in London.
In other futures trading, wholesale gasoline fell 2.4 cents to close at $1.828 a gallon, while heating oil fell 2.5 cents to close at $1.630 a gallon. Natural gas fell 4 cents to close at $2.776 per 1,000 cubic feet.
Precious and industrial metals futures closed broadly lower. Gold lost $8.60 to $1,085.50 an ounce, silver gave up 21 cents to finish at $14.48 an ounce and copper edged down less than a penny to $2.38 a pound.
The price of U.S. government bonds rose slightly. The yield on the 10-year Treasury note fell to 2.26 percent from 2.27 percent late Thursday.