GARDAI uncovered a cannabis growhouse after keeping surveillance on a property for several days.
Gardai from the Roscommon Divisional Drug Unit and the local Detective Unit raided a shed behind a home in Athleague on Tuesday afternoon.
Up to 380 plants were discovered in the raid, with an estimated street value of around €300,000. A man in his 30s was arrested.
He is being questioned at Roscommon garda station. Investigations are continuing.