The amount of cash market participants are borrowing to buy up more stocks continues to climb to record highs, leading some to grow increasingly concerned that a market pullback could be around the corner.
This borrowing - known as margin debt – occurs when stock brokerage firms lend to their investors to fuel more spending on securities and has risen to "uncharted territory" on the New York Stock Exchange (NYSE), according to U.S-based research company TrimTabs.
"Bears beware," said TrimTabs chief executive David Santschi in a research note on Monday. "Rising margin debt is a bullish indicator in the TrimTabs Demand Index this week."
(Read more: Playing with fire? Margin debt most since crisis)
The indicator climbed to $452 billion in January, it said, the seventh consecutive month of all-time highs. It increased by 1.4 percent from December, 36 percent from an interim high of $381 billion set in July 2007, and has rallied 63 percent from the interim low of $278 billion set in July 2012. Margin debt has almost doubled on the NYSE since the start of 2000.