A prison officer and inmate from Mountjoy were hospitalised today in the second violent incident in the jail this week.
The pair were injured after officers tried to intervene in a row between two inmates.
Other prisoners refused to leave the area and the prison had to be locked down, although authorities said this was normal procedure at lunchtime.
Meanwhile an inmate who was beaten about the head by another prisoner in a row over a TV remote control remains in serious condition.
A Prison Service spokesman said: “One prisoner and one prison officer have been brought to the Mater hospital as a precaution.
“It’s a minor incident. It’s not connected to the previous incident.”
Yesterday a 26-year-old prisoner was rushed to hospital with head injuries after being attacked the previous night by an inmate with a sock stuffed with batteries in a row over a TV remote control.
The injured man was brought to the Mater hospital but later discharged himself and returned to the prison.
The next morning the Prison Service said he was difficult to wake and he was rushed back to the Mater.
The Prison Service and gardaí have launched two separate investigations into the incident.
Prison officers have frequently raised concerns about overcrowding in the Dublin prison, in which inmate Gary Douche was beaten and killed in August 2006.
Fine Gael Justice Spokesman Charlie Flanagan said the latest attack was a symptom of chronic overcrowding in the State's prisons.
"Any attack on a prison officer is extremely serious and a terrifying ordeal for the victim involved. However, the conditions in our prisons have created a tinderbox and it is sadly unsurprising that violence has erupted," he said.
"Our prison system is an abject failure. It does not prevent crime but rather sees half of offenders back inside within four years. The State imprisons the homeless and the mentally ill, without dealing with the root cause of either problem. The haphazard approach to prison policy has created dangerous conditions in many prisons, Mountjoy being the most dangerous of all."
He accused Minister for Justice Dermot Ahern of failing to take any action to prevent violent incidents occurring, describing it as a "damning indictment" of his record.
PA