FOUR men were arrested and two were hospitalised after a disturbance in Valley.
Five people were injured during the incident at in the early hours of Saturday morning, including two men from outside the region, who were taken to Ysbyty Gwynedd in Bangor with serious facial injuries.
Detectives have urged anyone who saw the disturbance, or who has any information, to come forward.
Detective Constable Gerallt Jones of Holyhead CID said: "Police were alerted to the disorder at around 1.45 am and although it occurred during the early hours, a significant amount of traffic travels through Valley - mainly from Holyhead.
“Therefore, it is very possible that passing motorists or people returning from a night out would have seen the incident."
The four men arrested, have been released on police bail pending further enquiries.
Anyone with information should contact Holyhead CID on 101. Alternatively, call Crimestoppers anonymously on 0800 555 111.