Up to 5,800 cannabis plants worth about 4.6 million euro have been seized during a series of raids.
Eight men are being questioned over the discovery of six grow houses at industrial units and commercial premises across the country on Wednesday.
Gardai said the searches were carried out as a part of Operation Nitrogen, an intelligence-led operation by the Garda National Drugs Unit targeting the cultivation of cannabis. The suspects, who are believed to be from Asia, are being questioned at various garda stations nationwide.
:: Four men were arrested when a large cannabis cultivation operation, with approximately 1,700 cannabis plants worth an approximate street value of 1.36 million euro, pending analysis, were found in an industrial unit on Connaught Road in Longford.
:: About 1,000 plants worth 800,000 euro were discovered in an industrial unit at Cornafulla, Athlone, Co Westmeath. One man was arrested at the scene.
:: A search of an industrial site in Drogheda Business Park, Co Louth, uncovered 1,600 cannabis plants with an approximate street value of 1.28 million euro. Two men were detained.
:: One man was taken in for questioning when 1,000 plants, worth about 800,000 euro, were found at a commercial site in Campile, Co. Wexford.
:: In industrial unit in Kiltimagh, Co Mayo, 500 plants, with an estimated street value of approximately 400,000 euro, were seized. There were no arrests.
Elsewhere, cultivation equipment was seized in a residential house in Foxborough Hall in Lucan, Co Dublin. No plants were found. All of the suspects can be detained for up to seven days under Section 2 of the Criminal Justice (Drug Trafficking) Act, 1996 as amended.