Two more medics at Blackpool Victoria Hospital have been arrested by detectives investigating the suspected poisoning of patients on the stroke unit.
The man and a woman were held on suspicion of "administering any poison or noxious thing with the intent to injure and ill treatment or wilful neglect", police said.
They were in custody this afternoon.
A third person, a female nurse, was arrested last month and last week re-bailed until Sunday, February 10 next year.
All three NHS workers were suspended by the hospital, which flagged concerns with police the day before the first medic was arrested.
A "number of post-mortem examinations" have also been carried out, police said, though a spokesman said he was unable to say how many, or how many alleged victims have been identified.
Det Ch Insp Jill Johnston said: "We have made two more arrests as part of an ongoing investigation into allegations of mistreatment of patients at Blackpool Victoria Hospital.
"This is a complicated and sensitive inquiry which remains at its early stages.
"I understand further arrests might be concerning but I would like to reassure people we have a dedicated team of detectives working on this investigation.
“We are offering support to those families who have had loved ones identified as potentially being involved.
"They are being kept fully updated and supported throughout the process by specially-trained officers.
“Some post-mortem examinations have been conducted to assist our enquiries."
She said the priority was to "ensure the safety of patients", with police working "closely" with the hospital and coroner.
Boss Wendy Swift last month said "all allegations of this type" are taken "extremely seriously", and said she wanted to "reassure all our patients that all necessary actions are being taken".
She added this afternoon: "We can confirm two further healthcare professionals, who had been suspended following allegations of mistreatment against patients on the stroke unit, have been arrested.
“We take all allegations of this type extremely seriously and when the concerns were raised we immediately contacted the police.
“The trust is continuing to work with the police and co-operate fully with their investigation.
“We would like to reassure all our patients that all necessary actions are being taken. The hospital remains a safe and caring environment for patients and the provision of services will continue as usual.’’
When asked how many patients, if any, are known to have been hurt, and how many families were being contacted, a spokesman previously said there would be no further statement.