Caterpillar drove the Dow Jones industrial average higher Friday after the company reported a huge gain in first-quarter earnings.
The world's largest maker of mining and construction equipment rose 2.5 percent after its earnings increased more than fivefold. The company also raised its sales and profit forecast for the year.
The Dow added 4 percent in April, its best month since December.
The Dow rose 47.23 points Friday, or 0.4 percent, to close at 12,810.54. Caterpillar accounted for 21 points of those gains. The company's stock has soared over the past year on booming demand for its products.
"The industrial sector and the manufacturing sector of this country are much stronger than many investors have perceived," said Rob Lutts, president and chief investment officer of Cabot Money Management.
The Standard & Poor's 500 index rose 3.13 points, or 0.2 percent, to close at 1,363.61. The index gained 2.8 percent in April.
The Nasdaq composite added 1.01 point to 2,873.54. It rose 3.3 percent for the month.
Both the Nasdaq and the S&P 500 had their best month since February.
Strong corporate earnings pushed major stock market indexes to 2011 highs in the last week of the month. On Wednesday, the S&P 500 doubled from its 12-year low reached on March 9, 2009, after the financial crisis. The Nasdaq is at its highest level since 2000.
The Russell 2000 index of small stocks also hit a record high on Wednesday after the Fed pledged to keep short-term interest rates at record lows. That motivated investors to continue buying risky investments such as small stocks.
The Russell has soared 77 percent over the past two years. Small-company stocks tend to rise more quickly than the overall market as the economy emerges from a recession. Investors also see them as likely takeover targets for larger companies that are flush with cash. The Russell rose 3.74 points, or 0.4 percent, to 865.29 Friday.
Goodyear Tire & Rubber Co. rose 12 percent, the most of any company in the Standard & Poor's 500 index, after it set a company sales record and reversed its loss from the first quarter of last year.
Coinstar Inc. rose 5 percent after the owner of Redbox DVD rental kiosks posted a 32 percent increase in its net income.
Research In Motion Ltd. fell 14 percent after the maker of the BlackBerry slashed its earnings and sales forecasts because of weak phone sales.
The dollar fell to a three-year low against an index of six major currencies. It's down 7.6 percent this year.
The dollar has been sinking against other currencies that have higher interest rates than the United States. Low interest rates in the U.S. also encourage investors to borrow in dollars to buy investments denominated in other currencies, which also pushes the dollar lower.
Two stocks rose for every one that fell on the New York Stock Exchange. Trading volume was 3.7 billion shares.