A prisoner in Mountjoy Prison is challenging the conditions in which he is being held.
Ian Merriman, from Dublin, is at the beginning of a two-year sentence for burglary.
He is being detained in a cell in the basement of Mountjoy Prison in an area known as 'the Base'.
His lawyers told the high court this afternoon, that up to twenty people were being held in the cell, which is meant to hold just six people.
The court was told the cell has no beds, no running water, and only one toilet, which is blocked.
Mr Merriman says he has not had a shower or a shave for two weeks.
The court heard that while the prisoners are allowed out at certain times for exercise, they spend most of their time crammed into their cell, in the heat.
The case will be heard again on Monday, when the authorities responsible for Mountjoy Prison will have a chance to respond.
