CHAPEL HILL - The campaign headquarters of Democratic presidential candidate John Edwards reopened today after authorities determined that the white powder found in an envelope wasn't dangerous, campaign officials told The Associated Press.

Edwards said a letter in the envelope contained "some negative comments" and powder spilled out of the envelope, but he didn't elaborate on what the letter said or its possible source.

Preliminary testing found that the powder contained no chemical or biological agents, said Jane Cousins, a spokeswoman for the Chapel Hill police. Further testing will continue for the next several days.

"It's like any high-profile presidential campaign, you're going to encounter threats and these kinds of instances," Edwards said during a conference call before a scheduled speech at St. Anselm College in New Hampshire.

The office was evacuated Wednesday afternoon after a worker there opened the envelope.

The discovery prompted an investigation by local police, firefighters, the FBI, the Hazardous Materials Regional Response team from Raleigh, and the Orange County Health Department.

It was unclear where Edwards, who recently moved to Orange County, was when the letter was opened. He is scheduled to be in New Hampshire today.

A woman working in Edwards' campaign office in Southern Village found the powder at 4 p.m. as she opened mail for the former senator. She immediately threw the white legal-size envelope into a nearby mail bin and rushed to wash her hands, Cousin said.

Police were called to the office at 410 Market St. in the mix of offices, shops and homes in the southern Chapel Hill community. Federal, county and regional investigators were called to assist.

By late Wednesday, the envelope had been taken to the parking lot of the Chapel Hill Police Department several miles away on Martin Luther King Jr. Boulevard.

White powder in letters has been associated with anthrax since an attack in 2001 killed five people and sickened 17. The substance was mailed to lawmakers on Capitol Hill and members of the news media in New York and Florida just weeks after the Sept. 11, 2001, terrorist attacks.

The Edwards campaign worker did not know to whom the envelope was addressed or where it was from, investigators said. Chapel Hill police said they didn't know whether there was any written message in the envelope.

Police lauded the woman's swift response to the suspicious mail.

"Everything's been contained," Capt. Bob Overton of the Chapel Hill Police Department said several hours after the call came in. "They did exactly what they should; it was textbook. You divest yourself of the package, wash your hands and call the authorities."

— The Associated Press contributed to this story.