A 59-year-old man from York has been arrested on suspicion of murdering missing chef Claudia Lawrence.
The man is being questioned about 35-year-old Miss Lawrence's disappearance in the city in 2009. He has been named locally as Michael Snelling.
North Yorkshire Police have been carrying out forensic examinations at Mr Snelling's house in Burnholme Grove.
A house in North Shields, Tyneside, is also being searched as part of the investigation.
Police have also seized a car and said further arrests could not be ruled out.
Forensic officers have boarded up the property as part of their investigations at the house in York.
Miss Lawrence, who lived in Heworth, worked at the University of York.
She was due to start a 06:00 shift there, but failed to turn up.
She was reported missing by her father, Peter, 67, the following day.
Extensive searches of the area were made, but she was not found and police have since treated her disappearance as murder.
North Yorkshire Police launched a review of the case last year and have carried out new forensic work and searches of Miss Lawrence's home.
A fresh appeal for information was made on the fifth anniversary of her disappearance in March, which was broadcast on the BBC's Crimewatch programme.
Police revealed several new lines of inquiry generated by the review of the case and a fresh examination of her home.
Fingerprints had been uncovered using techniques not available in 2009, they said.
A DNA profile of a man was also found on a cigarette end discovered in Miss Lawrence's Vauxhall Corsa.
North Yorkshire Police said the Lawrence family had been informed of the arrest and were being offered support.
Claudia's mother, Joan, said the arrest was a "total shock".
"I am totally amazed and I haven't really got my head round it," she told BBC Radio York.
Mrs Lawrence, who lives in Malton, had criticised the original investigation into her daughter's disappearance.
"They were focussing on just one thing like old boyfriends coming out of the woodwork," she said.
"This is the first time we have been listened to and look what has happened since the new investigation started."
Miss Lawrence's close friend Suzy Cooper said she always believed there would be progress.
"For five years that has been really frustrating," she said. "It feels more tangible now there is an arrest."
Martin Dales, a spokesman for Claudia's father Peter, said he was "very encouraged" by the news of the arrest.
"It is the first time anyone has been arrested in the whole five and a bit years Claudia has been missing," he said.
"Peter and the family want answers and they need some closure. If this is leading in that direction then that will be welcome."
The BBC's North of England correspondent Danny Savage said: "This is by far the most significant development in this inquiry in five years. It seems now that progress is finally being made."