Via NY Times:

A letter addressed to Mayor Michael R. Bloomberg that arrived late last week at a municipal building has tested positive for ricin, according to two people familiar with the matter.

A second letter containing the poison arrived at a building in Washington that houses Mayors Against Illegal Guns, a group Mr. Bloomberg helps run and finances, a person familiar with the matter said.

Mr. Bloomberg never received the letter addressed to him, and there is no indication that anybody has become ill as a result of the two letters, those familiar with the matter said.

The letter sent to Mr. Bloomberg arrived at 100 Gold Street, which houses the offices of the Department of Housing Preservation and Development.

Ricin can be fatal if swallowed or inhaled.