Detectives investigating the disappearance of Melanie Hall in Bath in 1996, have been granted an extra 12 hours to question two men in connection with the case.
Miss Hall has never been found
The pair, in their 30s, were arrested in the early hours of Wednesday morning.
Police now have until 1800 GMT on Thursday to either charge them, release them or apply to magistrates for a further 24 or 48-hour extension.
Melanie Hall disappeared after leaving Cadillacs nightclub in Bath in June 1996.
Police began searching several locations in and around the Bath area on Wednesday and are continuing their hunt.
Miss Hall, then 25, from Bradford-on-Avon, Wiltshire, disappeared in the early hours of Sunday 9 June after a night out at Cadillacs nightclub in Bath.
The hospital clerical worker has never been found.
Police are searching farmland at Inglesbatch
Police have confirmed that neither of the men arrested was Miss Hall's boyfriend.
Earlier, 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.