Always adds risk.

Investors borrowed another record amount against their brokerage accounts in November, as so-called margin debt rose for a sixth straight month.

Last month, investors borrowed $423.7 billion against their portfolios, exceeding October’s record of $412.4 billion, according to the New York Stock Exchange. The Big Board’s member brokerage firms report the level of borrowing, known as margin debt, held against client accounts monthly.

Margin-debt levels rose 2.7% from the prior month. The gain coincided with the Dow Jones Industrial Average’s 3.5%.

Rising levels of margin debt are generally seen as a measure of investor confidence, as investors are more willing to take out debt against investments when shares are rising and they have more value in their portfolios to borrow against.

With margin debt, investors pledge securities—stocks or bonds—to obtain loans from their brokerage firms. The money doesn’t have to be used to just make more investments. The funds can be used in whatever way the account holder wishes.

But some see the increase as a sign of speculation, particularly if the borrowed money is reinvested in stocks. And some market-watchers have gotten wary that investors buying into stocks now are chasing a rally, which lends to the argument that stocks are moving closer to bubble territory. The S&P 500 is up 27% this year and finished Friday at a record high, its 41st of the year.

Peter Boockvar, managing director at The Lindsey Group, notes total margin debt stands at about 2.5% of nominal GDP. That compares to 2.6% of GDP in July 2007 and about 2.8% in March 2000.