More than 150,000 so-called party pills have been seized by the drugs squad, gardaí said today.
The BZP or Benzylpiperazine tablets were found in a suitcase after a car was stopped and searched in Rathmines, south Dublin on Sunday.
A follow-up search of a flat in the area recovered more of the same illegal stimulant pills.
Gardaí said the haul has a street value of more than €700,000.
Three men, aged 25, 21 and 20, were arrested following the searches and one has been charged.
BZP, once promoted as a legal alternative to ecstasy and amphetamines, was banned in March this year.
The man-made chemical pills had been widely sold in head shops.