In a brief statement, the Portland Police Bureau did not say why it was reopening the investigation. Police earlier said they considered the case closed because there was no evidence.
A spokeswoman for Gore said the former vice president "unequivocally and emphatically" denied making unwanted sexual advances toward the woman and that he welcomed the investigation.
"Further investigation into this matter will only benefit Mr. Gore," spokeswoman Kalee Kreider said.
She also said "the Gores cannot comment on every defamatory, misleading and inaccurate story generated by tabloids."
The massuese alleges Gore made unwanted sexual advances during a massage appointment on Oct. 24, 2006, at the downtown Hotel Lucia, where Gore was reportedly registered as "Mr. Stone." Gore was in Portland to deliver a speech on climate change.
The story first broke when the National Enquirer reported the allegations a week ago.
Portland police last week said the woman's lawyer came to them with the allegations in 2006 but that the woman canceled appointments with detectives. The case reopened in January 2009, when detetectives interviewed the woman but determined there was insufficient evidence to support the allegations.
According to transcripts of the 2009 interview, the masseuse described the allegations at length. She said Gore groped, kissed and pinned her down on a bed. She told Gore he was acting like a "crazed sex poodle," according to the transcript.
Gore and his wife announced June 1 they were separating.
