The men - aged in their 50s - are being held at Clontarf and Ballymun Garda Stations
Two men have been arrested by gardaí investigating the murder of David Byrne.
Mr Byrne (33) was shot dead in February when an armed gang burst into a boxing weigh-in at the Regency Hotel in Dublin.
Gardaí say one man was arrested yesterday evening and another was arrested this morning. They are both in their 50s.
They are being detained at Clontarf and Ballymun Garda Stations.
There have now been a total of seven people arrested in relation to the investigation.
Patrick Hutch (24) became the first person to be charged with the killing earlier this month.