All investors know they are taking a chance when buying stocks or mutual funds, but now one money market -- the safest of all stock investments -- has done something once unthinkable and actually lost money.
The Reserve Fund's Primary Fund, the very first money market mutual fund ever established, had its value fall below $1 this week, thanks to investments in now-bankrupt Lehman Brothers. Investors who put money there as a safe haven from the market's turmoil are now realizing a 3 percent loss.
The shortfall is nothing compared to the double-digit plunges many stocks have taken this year, but the whole idea behind money markets is that they should never lose money and fall below $1 a share. Falling below $1 is called "breaking the buck."
Unlike bank accounts, money market investments are not insured by the Federal Deposit Insurance Corporation or any other agency. Brokerages have always said that they carry risk but a widely held understanding is that they will not lose value.
Fidelity, Vanguard and other major fund mangers prominently posted messages on their Web sites this week trying to reassure investors of the stability of their money market accounts.
Analysts, personal finance advisers and other fund managers all said this was an isolated incident and should not reflect on the health of other money market accounts.
In fact, the decline in the Primary Fund is only the second time in history when such a fund has actually lost money. The other instance was in 1994 when the Community Bancshares fell. The fund was liquidated and investors ended up losing about 4 percent of their money.
"The fundamental structure of money market funds remains sound. These funds are subject to strict regulation governing credit quality, liquidity, diversification and transparency," the Investment Company Institute, the industry's trade association, said Wednesday.
Overall, there is $3.6 trillion invested in money market funds, according to Mike McNamee, spokesman for the group.
Nearly $1 trillion have come into the fund in the last year as people have moved their money away from stocks in this unstable market.
There are more than 800 money market funds out there and 33 million households invest in them.
David McPherson, founder and principal of Four Ponds Financial Planning and an ABC News personal finance columnist, said small investors should pay attention.
"The vast majority of money market fund holders do not need worry about it, but they should pay attention to what is happening, if anything, to understand how money market funds work," McPherson said.
Money markets are used by people waiting to put their money into other stocks later or very conservative investors near retirement. McPherson said many of his retired clients have large sums of money in such funds.
"If you do see a money market fund that is paying quite a bit more than other money market funds, that's something you need to question why," he said. But he noted, "A top firm like Vanguard or Fidelity is going to do everything possible, within their power, to avoid breaking the buck with their money market funds."
Lawrence J. White, an economics professor at New York University's Stern School of Business, said such failures are "highly rare."