State Street Global Advisors launched five bond exchange-traded funds on the American Stock Exchange on Wednesday.Three of the new State Street SPDR ETFs track Treasury bond indices of various maturities, one tracks an inflation-protected securities index, and another tracks an investment-grade bond index. SSGA, a unit of State Street ( STT), was the first to market with a stock ETF 14 years ago when it launched the Standard & Poor's Depositary Receipt ( SPY), also called the SPDR. But the company has been relatively slow out of the starting gate with bond ETFs; its first five offerings follow on the heels of two other providers: Barclay Global Investors, a unit of Barclays PLC ( BCS ) and Vanguard. Still, the fixed-income asset class is relatively untapped by ETFs, which are essentially index-oriented funds that trade on an exchange. With the five launched Wednesday, the total number available in the U.S. has more than quadrupled over the past five months to 25. At the end of 2006, there were only six bond ETFs, all of them BGI's iShares. Since then, BGI has almost tripled its offerings. Vanguard got into the game in April with four bond offerings. "We've been working on a fixed-income product for years," says Gary MacDonald, State Street's director of marketing. "But the regulatory environment was hard." He says it can take a long time to get approval the Securities and Exchange Commission to sign off on a new ETF, though the process has been getting better.