Exchange-traded funds that amassed junk bonds at a record pacein the first half of 2012 are now attracting unprecedented cash tobuy speculative-grade loans as investors wager that a four-yearrally in the notes is ending.

Blackstone Group LP, the world's largest private-equity firm, isplanning its first ETF that will mostly buy loans, and PyxisCapital LP, spun off from Highland Capital Management LP, announcedits first such fund last week. Invesco Ltd.'s PowerShares SeniorLoan fund, started two years ago as the first ETF solely dedicatedto loans, has grown to become the third- biggest speculative-gradedebt ETF with $1.2 billion of assets.

ETFs, which allow investors to speculate on securities withoutactually owning them, are shifting into floating-rate senior loansas concern mounts that junk bonds are losing momentum after gaining114 percent since 2008. The gap between yields on bonds and loanshas fallen to less than half the historic average amid the FederalReserve's actions to stimulate the economy.