Gardaí arrested 43 people at a disco in Co Monaghan, early yesterday morning.
A team of undercover gardaí, most of whom were attached to the Garda Drugs Unit, mixed with 4,000 revellers attending the disco at the Oasis Hotel, outside Carrickmacross.
Uniformed gardaí moved in, as members of the plainclothes unit made 39 seizures of cocaine, cannabis, acid, speed and ecstasy in an operation that lasted 12 hours. All those detained have since been released and files are being prepared for the DPP.
The value of the drugs seized was being assessed by the authorities yesterday.
Garda Supt. Tom Long of Carrickmacross, who was in charge of the operation, said: "This was one of the most co-ordinated anti-drugs trafficking operations in the region."
He said it was designed to curb cross-Border drug-trafficking in the region and target the "drugs culture" which caused serious concern in Border counties.
A number of those detained are understood to be from counties Monaghan, Cavan, Meath, Armagh, and the Dublin area. The operation involved Garda units from the Cavan/Monaghan Division, Sligo/Leitrim Division and the Garda National Drugs Unit.