Hundreds of thousands of archaeological items recovered from historic sites in Northern Ireland are lying unclassified in plastic bags and boxes.
They are often being kept outside the jurisdiction because there is no proper facility to store them.
One estimate says up to 24 container loads of archaeological objects are being stored by private companies.
The Institute of Archaeologists in Ireland (IAI), said it was "a very serious problem".
It said no tangible progress had been made to find a solution.
The BBC got access to one of the storage facilities in Kells, County Meath, in the Republic of Ireland, where hundreds of boxes of ancient pieces of bones, pottery and flints - many recovered in Northern Ireland - are stockpiled to the ceiling.
Developers pay for any archaeological digs. During the building boom, there was a record amount of road and houses building. But when the recession hit and some companies folded, the money dried up.
As a result, material was left sometimes unprocessed in warehouses in the Republic of Ireland and in other parts of the UK, and storage is now paid by the private companies.
Objects uncovered in Northern Ireland are also being kept elsewhere because of a lack of a suitable storage facility.
Eoin Halpin, director of the company Archaeological Development Services, said: "The Northern Ireland Executive needs to understand the nature of the problem. They should find a store or an archive for this material.
"It's part of their state's responsibility - it needs to be looked after. This material needs to be stored in some depository that is supplied by the state. This material needs to be taken away and needs to be analysed."
Mr Halpin said private companies like his could not be expected to pay for the cost of storing the items indefinitely.
"I'm passionate about this material and this material can't be allowed just to end up in a skip," he said.
It cost millions of pounds to dig the material out of the ground, but because of storage problems, neither students nor the general public can access them.
The Stormont Executive needs to embark on "a rethink of legislation, organisation and oversight" if Northern Ireland is to be a place where excavations are undertaken "in the secure knowledge that artefacts and written and drawn records produced will be properly treated," the IAI has said.
At the warehouse in Kells, about a third of the hundreds of boxes of exhibits came from archaeological digs in Northern Ireland in recent years.
Some of the material stored there includes 6,000-year-old samples from the Neolithic period removed from a dig site in Broughshane, County Antrim, 10 years ago.
"Most artefacts and archives are currently in the possession of commercial archaeological companies which are based not only in Northern Ireland but also in the Republic of Ireland, Scotland and England," said Rob Lynch from the IAI.
Mr Lynch said he feared the material could end up being damaged.
"Northern Ireland remains alone in its failure to provide the government-funded storage facilities necessary to ensure the proper long-term preservation and adequate curation of this valuable and finite archaeological resource," Mr Lynch said in a letter of complaint written to the Department of Culture, Arts and Leisure (DCAL) committee.
"It is a matter of regret also, that successive ministers in DCAL have failed to address the problems caused in this area by the withdrawal of National Museums Northern Ireland from the leading role, formerly played by the Ulster Museum, in promoting and working to best practice in conservation, curation and long term storage."