A 37-year-old man is being treated for chest wounds after being attacked with a nail gun during an attempted robbery.
The assault happened on Sunday evening in Sinope Street, Gloucester, but the three offenders escaped empty-handed.
The victim was taken to Gloucestershire Royal Hospital where his condition is said to be stable.
The three men were aged between 17 and 20 and all about 5ft 8ins. Two wore black and white checked bandanas and black and white baseball caps.
All three wore baggy jeans.
Police are appealing for witnesses to the attempted mugging, which happened at about 1940 BST on Sunday.