Detectives are questioning a woman about the discovery of drugs and a firearm.
The find was made during a raid on a house in Mahon, Cork, on Wednesday night.
Cannabis herb with an estimated street value of 30,000 euro was seized, along with a gun.
The haul has been sent for forensic tests.
A 26-year-old woman was arrested at the scene.
She was taken to Cork's Bridewell Garda station where she is being held under the Drug Trafficking Act.
A Garda spokesman said: "Investigations are continuing."