A man suspected of inflicting fatal head injuries on a man in his 40s at a social gathering in a house in Kilkenny City remained in Garda custody on Friday night.
The dead man has been named locally as Liam Edward O’Sullivan, a 46-year-old father of five.
Gardaí said all the resources of a murder investigation have been committed to the case.
Mr O’Sullivan was assaulted at a house at High Hayes Terrace, Castlecomer Road when a dispute flared at about 4am on Thursday.
He suffered serious injuries and was taken by ambulance to St Luke’s Hospital, where he was pronounced dead on Thursday night.
A postmortem was completed on Friday. The results have not been released for operational reasons.
A man in his 30s and a woman in her 20s were arrested on Thursday by gardaí in Kilkenny under Section 4 of the Criminal Justice Act.
The woman was released without charge after a short period of questioning but the male suspect remained in custody late on Friday night.
The scene of the attack was sealed off by gardaí in the early hours of Thursday. It has undergone examination by the Garda Technical Bureau and is expected to remain sealed off on Saturday.