Three Senate office buildings were closed Tuesday after a suspicious white powder, apparently delivered through the mail system, was found in the Senate majority leader's office. Officials said several preliminary tests - but not all of them - were positive for ricin, a deadly poison.

A white powder found in Senate Majority Leader Bill Frist's office tested Tuesday as an "active" form of the deadly poison ricin, forcing cancellation of most Senate business in the second such scare from a lethal toxin to hit the capital.

Three Senate office buildings were closed Tuesday after a suspicious white powder, apparently delivered through the mail system, was found in the Senate majority leader's office. Officials said several preliminary tests - but not all of them - were positive for ricin, a deadly poison.

Three Senate office buildings were closed Tuesday after a suspicious white powder, apparently delivered through the mail system, was found in the Senate majority leader's office. Officials said several preliminary tests - but not all of them - were positive for ricin, a deadly poison.

Senate Majority Leader Bill Frist said Tuesday that a white powder found in his office tested positive for the deadly poison ricin, forcing closure of Senate office buildings and close scrutiny of congressional mail. It was the second such scare from a lethal toxin to hit the nation's capital.