A man is being questioned today by gardaí investigating the death of a second man in Waterford city yesterday.
The suspect, in his 30s, was arrested in relation to the incident in Lower Grange.
It is understood the victim, in his 20s, was stabbed in the house yesterday afternoon.
He was taken to Waterford Regional Hospital where he died shortly after 5pm.
A post-mortem examination is due to be carried out later today.
The house and surrounding area were sealed off overnight and the State Pathologist called to the incident.
"The Garda Technical Bureau have arrived on site and will being a full examination of the scene at first light," said a Garda spokeswoman.
"The post mortem will be carried out today at 1pm."
The suspect is being detained at Waterford Garda Station under the provisions of Section 4 of the Criminal Justice Act.