According to police, three female employees who work in the mail room complained of itchy eyes and nausea. A manager notified police of the situation.
The employees were decontaminated before being taken to the hospital.
Authorities evacuated everyone from the building as a precaution, and a hazmat team began decontaminating the interior just after 10 a.m. Employees were allowed back into the building after 1 p.m.
Police say the package arrived Monday. It had an oily substance on its exterior and was isolated to the mail room.
The building where the package was delivered is also known as the Application Support Center and offers fingerprinting services needed after filing immigration papers. The only other ACS office is in Charlotte.
"All those tests at this point have been negative testing, but they are preliminary tests," Durham Police Department Captain D.C. Allen said. "They have recovered the package and it will be taken to the Public Health lab in Raleigh for some further testing."
HAZMAT teams apparently believed whatever was on or in the envelope was not at all dangerous and it was the fumes that made workers ill. Around 1 p.m. the crime scene tape was removed and the building reopened.
Police have not made a connection between this incident and Monday's incident at the capitol building, but they are investigating the possibility.
Monday evening authorities evacuated the state capitol after a staffer in Governor Beverly Perdue's office opened a letter that contained white powder. The powder tested negative for hazardous materials, according to preliminary results from the N.C. Division of Public Health.
Officials say the substance tested negative for hazardous materials. It was tested for anthrax, ricin and other bacteria, toxins and viruses.
The capitol remained closed to the public Tuesday as a precaution after the building was evacuated and closed Monday when the letter was opened.
Staff from the governor's office, State Capitol Police and the Department of Cultural Resources returned to work Tuesday.
State capitol police also opened a criminal investigation on Tuesday.
The capitol will reopen to the public on Wednesday.