A man in his 20s is understood to be in a critical condition following an incident in Monasterevin, Co Kildare, overnight.
Shortly after 12.30am, gardaí and emergency services were called to Dublin Road in the town following reports of an altercation involving a group of people at the entrance of a premises.
The man was found unresponsive at the scene and taken to Tallaght University.
A second man, aged in his early 50s, was treated at the scene for apparent facial injuries and taken to the Midlands Regional Hospital, Portlaoise. His injuries are not thought to be life threatening.
It is understood that both men are related.
The scene was preserved for a forensic examination and no arrests have been made.
Gardaí are appealing for witnesses following what they described as a "serious assault" on the two men.
Anyone with information is asked to contact Kildare Garda Station on 045 527730 or the Garda Confidential Line on 1800 666 111.
