Two inmates have died in separate incidents in Limerick and Wheatfield prisons over the last three days.
A 25 year-old man who was serving a sentence for manslaughter was found dead at 4am on Saturday morning in Limerick Prison.
His body has been taken to the Midwest Regional Hospital in Limerick for a postmortem.
Gardaí at Roxboro Garda station are investigating.
On December 24th a 23-year-old inmate of Wheatfield Prison was found dead in his cell. The man was in custody pending a court appearance in February.
A postmortem was carried out on his body in Tallaght Hospital.
It is understood both deaths were drug related.
A spokesman for the Irish Prison service declined to comment on the cause of the deaths but said in both cases there was no sign of foul play.
There are three separate investigations under way into each of the deaths involving the gardaí, the Irish Prison Services and the Inspector of Prisons.