Technology stocks are dropping for a second day in a row as investors flee high-flying Internet and biotechnology companies.
The Nasdaq composite closed its third losing week in a row.
The Nasdaq lost 54 points, or 1.3%, to end at 3,999. It was only the second time this year the index has closed below 4,000. It is down 8% from the high it reached in early March.
The Standard & Poor's 500 fell 17 points, or 1%, to 1,815. The Dow Jones industrial average fell 143 points, or 0.9%, to 16,026.
JPMorgan Chase fell 4% after reporting weaker earnings. Other big banks also fell, including Bank of America.
Bond prices rose. The yield on the benchmark 10-year Treasury note fell to 2.62%.