The 61-year-old woman who died in Co Mayo this morning had been stabbed a number of times.
She has been named locally as Carmel Marrinan, of Blackfort, Newport Road.
Ms Marrinan, a mother of seven, had worked as a nurse in a local nursing home.
Gardaí were called to her house on the Newport Road in Castlebar at around 3.45am this morning.
When they arrived, they found ambulance personnel attempting to resuscitate Ms Marrinan in the hallway.
She was brought to Mayo General Hospital but died a short time later.
A 29-year-old man was arrested shortly after 4am.
Gardaí are treating her death as suspicious and say they are following a definite line of inquiry.