A man has been arrested by police investigating the allegations of ill-treatment of patients at Muckamore Abbey hospital.
Detectives from the PSNI's Public Protection Branch detained the 25-year-old yesterday morning in the Antrim area.
No further details were given.
The man was the ninth person arrested in relation to alleged abuse at the hospital.
The Antrim hospital - which treats people with severe learning disabilities and mental health needs - has been the subject of a PSNI probe.
Police are investigating claims of physical and mental abuse of patients in the psychiatric intensive care unit between 2017-18.
It is suspected that 1,500 criminal assaults took place over a number of months in a ward with six beds in the hospital. Police have been reviewing thousands of hours of CCTV footage.
Last week, a 57-year-old woman was arrested and released pending a report to the PPS.
There have been 59 precautionary suspensions of staff.
Health Minister Robin Swann also confirmed a public inquiry will be held into alleged abuse at the hospital.
The inquiry follows two reports into the abuse at Muckamore - a serious adverse incident report and a recently-published review into the leadership and governance of Muckamore by Belfast Trust.