(Close): US stocks ended Monday mixed as investors turn towards Tuesday, when Federal Reserve chair Janet Yellen is set to testify in front of Congress.
The Dow Jones fell 23.60 points to 18,116.84, while the S&P 500, external index dipped 0.64 points to 2,109.66.
The tech-focused Nasdaq index rose 5.01 points at 4,960.97.
Shares in aerospace giant Boeing were the biggest fallers on the Dow, falling 2.3%, after Goldman Sachs cut its rating on the stock to "sell".
Canada's Valeant Pharmaceuticals International saw its shares jump 14.7% after it agreed to buy Salix Pharmaceuticals at the weekend in a deal worth $10.1bn. Shares in Salix fell 1.3%.
Investors will be keeping an eye on events in Greece. Last week, the country agreed to extend its bailout programme for four months, but it must come up with a list of reforms on Monday in order to secure a bailout extension.
