Nitrous oxide canisters worth more than €1.9m have been seized at premises in Meath and Dublin.
Revenue officers seized 59,135 canisters as part of an "intelligence led operation".
The canisters, which have a legitimate use in the catering industry, contain a psychoactive substance.
Revenue said it has the power to seize nitrous oxide canisters and other psychoactive substances when there are reasonable grounds for believing imported goods are not being used for legitimate purposes.
Yesterday's seizure is part of ongoing operations aimed at the "illicit trade in, and the importation of, psychoactive substances into Ireland", Revenue added.
Investigations are ongoing.