The FBI is investigating the letter, but fire officials found nothing hazardous in the building, officials say.
Fire officials say part of the federal court building in Philadelphia was evacuated for about an hour this morning after the discovery of a letter containing a threat about anthrax, but nothing hazardous was found.
Executive Fire Chief Richard Davison says crews responded to the courthouse in the city's historic district about 9:25. He says people had to leave the second floor, but those on other floors were allowed to remain.
Fire officials investigated and didn't find anything hazardous, so the all-clear was given about an hour later. People have been allowed back inside.
The FBI is investigating.