Two are being detained in Portlaoise and two in Tullamore.
Four men remain in custody this morning after gardaí seized drugs worth nearly €4 million in Laois yesterday.
The discovery was part of an ongoing investigation.
As part of the operation, gardaí stopped and searched a vehicle near Raheen in Laois at 9:15 yesterday morning.
Inside it they found cannabis herb and cannabis products with an estimated street value of €3.9 million.
Four men were arrested at the scene - two of them in their 30s are being held at Portlaoise Garda Station and the other two in their 40s at Tullamore Garda Station.
Gardaí say the find was part of an intelligence led investigation into the supply and sale of controlled drugs.