Decontaminating the nerve centre of US politics
Nearby streets were closed to traffic as fumigators used chlorine dioxide gas to neutralise anthrax spores. These were found in a contaminated letter, forcing the authorities to shut the building seven weeks ago.
At least five people have died in a mysterious series of anthrax attacks in the United States beginning a few weeks after the 11 September suicide attacks on New York and Washington.
Hundreds of workers from private contractors and federal agencies have been taking part in operations to remove anthrax bacteria from the Senate complex on Capitol Hill.
Police spokesman Dan Nichols said it would take about 15 hours to fumigate Mr Daschle's office.
'No danger'
"There is no danger to the public whatsoever," he added. He said it was not yet known when the Senate's Hart building would re-open.
The authorities believe that the anthrax spores in the building come from a letter to Mr Daschle, the Senate Democratic leader, or a similar letter mailed to another senator, Patrick Leahy, which was intercepted before delivery.
Investigators have yet to trace the source of the anthrax letters.
But they have said that an elderly woman who died from inhalation anthrax - the most serious form of the disease - was probably exposed through the mail.
Connecticut Governor John Rowland said traces of anthrax bacteria had been found on Friday in a letter only five kilometres (three miles) from the home of Ottilie Lundgren, who died on 21 November.
No direct connection has been established between that letter and the death of Mrs Lundgren, who was 94.
But Mr Rowland said her mail may been contaminated by contact with the anthrax letters sent to the senators.
"I don't think that anyone suspects that Mrs Lundgren was a target," he said.
"We all believe, again unscientifically because it's not proven, that she was a victim of cross-contamination."