A man suffered serious head injuries in an assault at a walkway near a car park, gardai said.
Detectives believes the victim, 49, was with another man at Richmond Parade in Sligo when a row broke out.
The injured man was found lying near a walkway connecting to the Stevens Street car park near the Garavogue River at about 9pm.
He was treated in Sligo General Hospital but later taken to Beaumont Hospital in Dublin where his condition was described as serious.
A Garda spokesman said: "It would appear that the injured party was in the company of another male at Richmond Parade when a dispute arose which resulted in the injured party receiving head injuries."
The spokesman said a number of witnesses had already come forward but officers were anxious to trace anyone else who may have been in the area between 6-7pm on Thursday night.