A man was doused in petrol and set on fire while he slept in a shop doorway in Grafton Street, Dublin, early yesterday.
The victim, in his 40s, suffered third-degree burns to his feet and legs in the incident.
Two milkmen making their early-morning deliveries saw what happened, put out the fire and called an ambulance.
His assailants, both in their early 20s, fled on foot in the direction of St Stephen's Green.
Gardaí said they believed the man had been drinking until approximately 3 a.m. He could not remember the incident in any detail and could not provide an accurate description of his attackers.
The milkmen who saved him said his assailants had tight haircuts and were wearing black-and-white shell suits.
The victim is receiving treatment for severe burns in St James's Hospital, Dublin.
Organisations representing the homeless said the attack highlighted the extent to which people sleeping rough were vulnerable to random acts of violence.
They cited the killing of homeless man Paddy Pepper, beaten to death after a drinking binge in St Stephen's Green last April.
Serious physical and sexual assaults on street dwellers in Dublin now occurred on a regular basis, a Simon Community spokesman said.
He added: "This incident is truly horrifying and unfortunately proves just how vulnerable people sleeping rough are. Between 200 and 300 people sleep out every night in the greater Dublin area, and they're at the mercy not only of harsh weather conditions but are also prone to physical attack, robbery and sexual assault."