Three men have been arrested on suspicion of murdering York University chef Claudia Lawrence.
Searches are being conducted which are expected to be ongoing over a number of days.
North Yorkshire Police said no further details about the arrests of the men in their fifties who are from York will be provided at this stage of the investigation.
It follows the arrest of another man aged in his 50s on 23 March, who remains on police bail while enquiries continue.
Lawrence was last seen on 18 March 2009 when she went home from work, speaking to her parents on the phone that evening. Friends raised the alarm when she failed to turn up for a 6am shift at work the next morning. Her body has never been found.
Detective Superintendent Dai Malyn, head of the police's major crime unit and the senior investigating officer in the Claudia Lawrence inquiry, said: "I urge everyone to again show restraint and patience while we carry out these very important enquiries. Your co-operation and support is greatly appreciated by the investigation team."