Washington

Plans for the US Senate's long-awaited debate on the regulation of human cloning have collapsed, after negotiations between senators over the terms of the deliberation broke down on 13 June.

The breakdown means that prospects of any US federal legislation on cloning being passed this year are receding, with the Senate unable to muster the necessary 60–40 majority for either an outright ban on cloning or a more restricted ban, favoured by many researchers, that would permit 'therapeutic cloning' for research purposes.

The Senate's main advocate of an outright ban, Sam Brownback (Republican, Kansas), will now try to force his fellow lawmakers to address the issue by amending unrelated bills with pieces of his legislation.

This is the strategy that he used last year to force Tom Daschle (Democrat, South Dakota), the majority leader in the Senate, to promise a vote on cloning this year. But Daschle and Brownback were unable to agree on terms for the cloning debate.

Although Senate procedures are arcane, some observers say that Brownback's new strategy is unlikely to succeed, especially as it appears to lack support from leaders of his own party. “The best way to get anything done in the Senate is to have a structured agreement on how it will be discussed,” says one lobbyist, adding that now “we have a free-for-all”.

A procedural vote to kill Brownback's first attempted amendment, which would attach a ban on the patenting of cloning procedures to an antiterrorism bill, was scheduled for 18 June, as Nature went to press. Even if he loses it, the Kansas senator is expected to mount periodic attempts to attach a cloning ban to other bills. The House of Representatives has already backed a total ban on human cloning, which is supported by President George Bush.