A 62-YEAR-OLD motorcyclist was ambushed and drenched in acid in a horrifying attack after he was mistaken for a member of a bikie gang.

The Pakenham man was rushed to Dandenong Hospital after the attack on the South Gippsland Highway near Bena earlier today.

He is in a serious condition after the unprovoked attack.

Police said the victim was ambushed by a group of men who screamed "we don't like bikies around here" as they attacked the man.

The victim was riding with a group of friends when they spotted another motorcyclists pulled over on the side of the road. The other motorcyclist got the man to pull over, then shoved him down the side of the embankment.

Police spokeswoman Sen-Constable Creina O'Grady said the man was trying to take his helmet off when a small green sedan pulled up and three men got out.

"One of the men then held up a bottle and squirted the victim with a chemical thought to be acid, causing serious burns to his eyes, face, chest and legs after burning through his clothes,'' she said.

"The three men and the motorcyclist then drove away heading towards Melbourne."

Police said they did not believe the victim was a member of an outlaw motorcycle gang.

Detectives have not spoken to the man but believe he did not know his attackers.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or visit their website at www.crimestoppers.com.au.

james.dowling2@news.com.au