A second excavation is being conducted at the site of a former mother and baby home in Tuam, Co Galway.
The tests were requested by the Commission of Investigation into Mother and Baby Homes.
The commission was established following allegations about the deaths of 800 babies in Tuam over a number of decades and the manner in which they were buried.
Last October, a preliminary excavation took place at the site.
Specialist archaeologists returned to Tuam in recent days and are expected to continue their work there for another two weeks.
It is understood the latest excavation will entail a more detailed examination of the grounds and will involve deeper excavations than those initially carried out last autumn.
Local historian, Catherine Corless, whose research brought the issue to light in 2014 says the ongoing investigation shows the importance being attached to the concerns of relatives of those who died at the home.
In addition to the inquiry around practices in Tuam, the commission is investigating 13 other mother and baby homes that operated in the State.
The inquiry is also examining a number of County Homes in Dublin, Cork, Donegal and Kilkenny.
It is due to conclude the process early next year, when a report will be furnished to the Minster for Children.