A man suffered facial injuries when an unknown substance was thrown at him in a suspected road rage attack on Teesside.
Police said the 44-year-old driver was treated in hospital after an altercation with another driver on the A1027 in Billingham at 07:00 BST.
A 19-year-old man has been arrested on suspicion of grievous bodily harm and possessing a weapon for the discharge of a noxious liquid.
Officers have appealed for witnesses.
A Cleveland Police spokesman said: "The incident occurred at around 7am when the driver of a white Mercedes A Class and a grey BMW were reportedly involved in an altercation.
"Both vehicles drove on, then pulled over and both drivers remained in their vehicles and had a verbal altercation.
"The 19-year-old male driver of the Mercedes allegedly then threw an unknown substance towards the 44-year-old male driver of the BMW.
"As a result, the driver of the BMW was taken to James Cook University Hospital where he is being treated for irritation to the skin on his face."