One man, 42, was taken into custody on Thursday after the car he was driving was stopped and searched shortly before 3pm in Rathnew, Co Wicklow.
Cannabis worth about €600,000 was discovered in a suitcase and he was detained at Pearse Street garda station.
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Later on Thursday a man aged 46 was arrested after gardai stopped and searched a car in Walkinstown, Co Dublin and found €85,000 in cash. He was also taken to Pearse Street garda station.
A follow-up search at a property in Dublin led to the seizure of €45,000 worth of cannabis and the arrest of one woman and three men.
The four were taken to Pearse Street and Kevin Street garda stations.
The searches were conducted as part of an operation into the sale and supply of illicit drugs.