A murder inquiry is expected to get under way after an elderly man was found dead in a psychiatric hospital.
Another man, in his 40s, has been arrested.
A Garda spokesman said the patient's body was found in the unit in Cavan at about 7am on Monday.
The suspect, also understood to be a patient at the hospital, was detained under Section 4 of the Criminal Justice Act at Cavan garda station.
A post-mortem examination is to be carried out later.
The Health Service Executive (HSE) said the incident happened in the Cavan-Monaghan Mental Health Acute Inpatient Unit in Cavan General Hospital.
In a statement, the HSE said it was examining all circumstances of the death and all appropriate procedures were being followed including informing the Mental Health Commission, as required by law.
"This is now a matter for the gardai and the HSE will be cooperating fully with garda investigations," the organisation said.
"The HSE is providing support to patients, their families and staff at this time. The HSE has expressed its sympathy to the family of the deceased."