A man suffered severe chemical burns to his face after he answered a knock at his front door and had acid thrown over him.
The 27-year-old victim suffered major burns to his face following the attack in Slough, Berks, last night.
Two other men who were in the house with him also suffered chemical burns to their hands and arms.
A spokesman for Thames Valley Police said: "We are appealing for witnesses following a grievous bodily harm incident in Slough.
"It happened at around 7.45pm yesterday when the offender knocked at the door of a property in Granville Avenue.
"The victim, a 27-year-old man, went to the door and the offender threw a corrosive substance at his face.
"He sustained severe facial injuries and remains in hospital in a stable condition.
"Two other men aged in their 20s, who were in the property at the time, sustained minor injuries to their hands and arms. They were taken to hospital and have since been discharged."
Investigating officer Detective Sergeant Lucy Deane of Force CID in Slough, described the incident as a "concerning" one and indicated that investigations were at an early stage.
"More patrols are in place and officers are currently in the area conducting inquiries so if you have any issues or concerns, please talk to the officers in the area or contact us," she added.
"We are asking for anyone with information about this incident to come forward and we would especially like hear from anyone who saw a black vehicle in the area.
"It is understood the offender may have used this vehicle to get to and from the property.
"At this stage it is understood to be an isolated incident. If you have any information that could help with this investigation, please contact the Thames Valley Police non-emergency number on 101.
"If you would like to remain 100 per cent anonymous, contact the independent charity Crimestoppers on 0800 555 111."
No arrests have been made in connection with the incident.
