The S&P 500 .SPX gained 2.78 points, or 0.11 percent, to 2,506.65, hitting its fifth record closing high in the last six sessions.
The Dow is up 37.20 points or 0.2 percent at 22,368.55, the Nasdaq is up 2.52 points or less than a tenth of a percent at 6,457.16 and the S&P 500 is up 2.55 points or 0.1 percent at 2,506.42.
USA stock index futures were little changed on Wednesday as investors awaited clues from the Federal Reserve meeting on whether the central bank will raise interest rates for a third time this year.
"Furthermore investors and speculators will be equally interested to hear what Fed Chairwoman Janet Yellen has to say about the prospect of another rate hike before the year is out".
"We had suspected that the recent softness of core inflation could persuade officials to hold off on the next rate hike until next year", said Andrew Hunter, US economist at Capital Economics.
"They will likely take on a more aggressive stance", Ablin said of the Fed, which could be seen as an endorsement of current economic conditions.
In line with expectations, the Fed said it would begin in October to cut its roughly $US4.2 trillion in US Treasury bonds and mortgage-backed securities holdings by initially cutting up to $US10 billion each month from the amount of maturing securities it reinvests.
Financial stocks have also moved to the upside on the day, while weakness visible among biotechnology and healthcare stocks.
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Advancing issues outnumbered declining ones on the NYSE by a 1.36-to-1 ratio; on Nasdaq, a 1.55-to-1 ratio favoured advancers.
Currently, the major averages are almost unchanged, showing moves of less than a tenth of a percent.
Also on the Dow, Caterpillar (CAT) climbed 1.9% and Boeing (BA) rose 1.4% on a positive day for industrials and materials groups. With the gain, the average reached a two-month closing high.
Gold again fell - down 1.2% to $US1,309 an ounce, while West Texas Intermediate oil futures (WTI) oil futures jumped to a touch under $US50 a barrel in NY.
In overseas trading, stock markets across the Asia-Pacific region turned in a lackluster performance during trading on Wednesday. Japan's Nikkei 225 Index inched up by 0.1%, while Australia's S&P/ASX 200 Index dipped by 0.1%.
Meanwhile, the major European markets moved to the upside on the day. While the UK's FTSE 100 Index edged down by 0.1%, the German DAX Index and the French CAC 40 both crept up by 0.1%.
The choppy trading on Wall Street comes as traders are waiting on the Fed's monetary policy announcement on Wednesday.