Recent accommodative policies from the Federal Reserve, European Central Bank and now Japan's central bank are seen as limiting downside, but concerns persist about Europe's debt crisis and slowing growth.
Those concerns limited Wednesday's equities gains and pushed the euro back towards $1.30 against a mildly stronger dollar.
"The feel-good factor from the Bank of Japan's move has worn off quickly and it's back to European matters," said Investec strategist Phillip Shaw.
Japanese stocks rallied to four-month high after the BOJ said it would increase its asset buying and loan program, currently its main monetary easing tool, by 10 trillion yen to 80 trillion.
European shares rose 0.2 percent. The MSCI index of global stocks also was up 0.2 percent.
U.S. existing home sales rose by their fastest pace in two years, the latest indication that a recovery in the housing market was gaining traction. An index of housing shares rose 2 percent.
The Dow Jones industrial average was up 16.29 points, or 0.12 percent, at 13,580.93. The Standard & Poor's 500 Index was up 0.70 point, or 0.05 percent, at 1,460.02. The Nasdaq Composite Index was down 4.86 points, or 0.15 percent, at 3,172.94.
The Bank of Japan action helped to offset concerns about tensions between Japan and China over a disputed group of islands in the East China Sea.
The dollar jumped to 79.21 yen, its highest since August 22, after the BOJ's decision. It last traded at 78.36 yen, down 0.6 percent on the day.
In the bond market, the benchmark 10-year U.S. Treasury note was up 11/32, with the yield at 1.7718 percent.
Oil prices sank to $108.98. Brent is down about 7 percent so far this week, though it remains up more than 11 percent over the past three months.