Masked men have stolen eight rhino horns from the National Museum of Ireland with a street value of about 500,000 euros.
The gang of three broke into the museum archives building in Dublin late on Wednesday, tied up a security guard and loaded four rhino heads - each with two horns - onto a van, police said.
The guard, who was unhurt, eventually freed himself and raised the alarm, but not before the thieves had made off with their haul.
Rhino horns have become increasingly valuable as a component of traditional medicines in Asia, where they are falsely believed to have powerful healing properties.
Poachers feeding the lucrative market have decimated rhino populations across Africa - in South Africa, more than 200 of the animals have been killed so far this year.
A spokeswoman for the Irish museum said fears about a possible theft had prompted curators to move the horns from public display last year into storage.
"Their price is based on weight and the total amount stolen could have a street value in the region of 500,000 euros," she said.