Detectives are investigating an assault in Colne which has left a man with a serious head injury.
Police were called to an incident in Market Street in the town at about 2-40am on Sunday.
When patrols attended they found a man in his 50s lying on the floor at the junction of Dockray Street and Market Street.
He was taken to Airedale Hospital and later transferred to Leeds General Infirmary. His condition is described as poorly.
An investigation is underway into the circumstances.
A 26-year-old man from Nelson was later arrested on suspicion of assault and is custody.