Two men have been arrested in connection with the disappearance of Melanie Hall in 1996.
Miss Hall has never been found
Miss Hall, then 25, from Bradford-on-Avon, Wiltshire, disappeared in the early hours of Sunday 9 June after a night out in Cadillacs nightclub in Bath.
The hospital clerical worker has never been found.
The men - in their 30s and from the Bath area - are being held at different stations in the Avon and Somerset area.
I would like to appeal again to local people to think back to the summer of 1996. There may still be someone out there who has yet to come forward
Detective Superintendent Barrie Douglas
Police have confirmed that neither of the men arrested was Miss Hall's boyfriend.
Steve and Pat Hall, Melanie's parents, said in a statement: "We have been told of the new information and the arrests that took place on Wednesday.
"It is far too early to know whether this will finally lead to the truth about what happened to our daughter.
"We hope this is the breakthrough the police need but we will wait and watch developments before commenting further."
An incident room has been set up with 40 officers at Kingswood Police Station, and a number of properties in the Bath area have been searched.
Detective Superintendent Barrie Douglas, who is leading the investigation, said: "This new information has hopefully allowed us to take forward the enquiry.
"However, I would like to appeal again to local people to think back to the summer of 1996.
"There may still be someone out there who has yet to come forward.
"To jog people's memories: on Saturday 5 June the Euro 96 football tournament hosted in England started," he added.