(Dow Jones) Investors fed up with U.S. stocks' negative returns and paltry rates in today's fixed-income markets are piling into exchange-traded funds that invest in high-yield corporate bonds.

"Where else can you get an 8% yield? The S&P 500 is flat over the last dozen years," said Matt Hougan, head of ETF analytics at IndexUniverse. "I'm not surprised people are looking elsewhere on the capital spectrum."

Still, investors need to be wary of the higher risk in "junk" bonds, which can manifest itself in big price swings relative to other categories of bonds. Structurally, Hougan noted the high-yield bond ETFs can trade at "significant premiums" to their net asset values. ETFs following less-liquid markets can see wider trading spreads.

Two high-yield ETFs with large asset bases-iShares iBoxx $ High Yield Corporate Bond Fund (HYG) and SPDR Barclays Capital High Yield Bond ETF (JNK)-both saw year-to-date inflows of more than $1.2 billion through July, according to data from the National Stock Exchange. More cash likely moved in the door this month amid a surge in bond issuance from corporate America.

The high-yield bond ETFs rallied in 2009 on easing economic and credit concerns, but are essentially treading water so far this year. The SPDR Barclays Capital High Yield Bond ETF gained 37.7% in 2009, according to investment researcher Morningstar Inc., as worries over defaults and bankruptcies eased. The fund lost 24.7% in 2008 as the credit storm raged. Both ETFs are currently yielding around 8%.

Hunting For Income 

The growth in high-yield ETFs is part of a wider rush to bonds as investors look for income while economic uncertainty causes gut-wrenching swings in the stock market. For example, more than $5 billion flowed into iBoxx $ Investment Grade Corporate Bond Fund (LQD) year to date through July 31. The ETF has a yield of 4%.

In the Treasury market, risk aversion and deflation fears are major factors pushing yields lower.

Last week, yields on 2-year notes dropped below 0.5% to the lowest levels on record. Yields on 10-year notes traded below 2.6%, and 30-year bond yields are sitting well under 4%. Yields and prices move in opposite directions.

Highlighting the flight-to-safety trade, the $3.4 billion iShares Barclays 20+ Year Treasury Bond Fund (TLT) has rallied nearly 20% so far this year.

Douglas Cliggott, U.S. equity strategist at Credit Suisse, in an Aug. 20 report, cited three forces that have driven 10-year yields below 3%.

"One is investors lowering their U.S. economic growth expectations. A second is good old-fashioned performance chasing. And the third, and perhaps the most important, is many Americans losing their appetite for risk," Cliggott wrote. "We believe the demand for U.S. financial assets with relatively high yields and relatively low volatility could remain elevated for several years."

Higher Yield, Higher Risk 

With six-month certificate of deposit rates averaging less than 1% nationally according to BankRate.com, it is no wonder many individuals are looking well beyond traditional savings accounts for income. The Federal Reserve has indicated it intends to keep short-term rates near zero to help stimulate the troubled economy and job market.

"The measly yields offered by the vast majority of fixed-income securities have forced investors to step up their hunt for current returns," said Michael Johnston, senior analyst at ETF Database. "For many, that search has led to junk bonds."

Although low rates have punished savers and investors approaching or in retirement who rely on income, they need to consider the risks of bond funds that are offering tempting yields, such those that invest in paper from companies that have lower credit ratings.

Investing in high-yield corporate bonds is "similar to investing in the equities of companies with highly leveraged balance sheets," said Morningstar ETF analyst Timothy Strauts.

In his latest report on SPDR Barclays Capital High Yield Bond, he said the ETF "should be viewed as a satellite holding, and a risky one at that." The fund takes an indexed approach with 166 holdings. The expense ratio is 0.4%, compared with 0.5% for iBoxx $ High Yield Corporate Bond Fund.

Some investors may be drawn to junk-bond ETFs because their yields are much higher than those offered by Treasury funds.

"With increased leverage comes the increased probability of default and bankruptcy," says Morningstar's Strauts. "In the grand scheme of things, risk equals return, and the 'high' yield of these bonds is designed to compensate investors for this risk."

Recently, there are signs volatility in equity markets "has taken its toll on retail investor enthusiasm about high-yield bonds," said Oleg Melentyev, credit strategist at Banc of America Securities LLC, in an Aug. 9 research note.

The strategist said inflows into the fund sector slowed to $50 million in the latest week, a "marked departure" from intakes of at least $500 million seen in each of the previous five weeks.

The volume of U.S. junk bonds has topped $155 billion this year and is on pace to break 2009's record, The Wall Street Journal reported earlier this month.

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