Drug squad garda officers are investigating the death of a 20-year-old man who collapsed after a night of partying.
Thomas Sheridan collapsed in a van as he was driven to his home in O'Maolchonaire Avenue in Donegal town on Sunday afternoon.
His parents made desperate attempts to revive him but he was rushed to Letterkenny General Hospital where he was pronounced dead on arrival.
A post-mortem examination took place on his body yesterday morning but gardai are likely to seek toxicology tests to determine what substances, if any, he had consumed which may have contributed to his death.
This is the second suspected drug-related death in Co Donegal in less than a week.
Five days ago, David Orr (30), from St Johnston, died after being brought in a collapsed state to a doctor's surgery in Letterkenny after attending a house party.
It could take months before toxicology results will become known in relation to his death.
Yesterday, officers from Donegal's drug squad joined the probe into the latest sudden death.
The victim is understood to have spent the night drinking in bars and attending house parties in Donegal Town and Mountcharles.
Officers also visited a remote mountain "shebeen", known locally as the Bog Hotel, to confirm whether this was one of the locations he had visited.
An unemployed labourer, the young victim had celebrated his 20th birthday less than two weeks ago.
Gardai said that they had questioned a number of people in their efforts to trace the young man's movements between late on Saturday night and 1.30 on Sunday afternoon when he was brought home.
Supt John Dennedy said gardai were satisfied they knew where the young man had been up until 8am on Sunday.
"There are some gaps from then until 1.30pm and I would appeal to anybody who may have helpful information to contact the gardai," he said.
He is believed to have attended a house party in the Mountcharles-Inver area.
Gardai also believe that he was at some stage in the company of a known heroin-user or former heroin-user which is the main reason for drugs officers' involvement in the investigation.
He is survived by his parents Tommy and Ann, older brother, Niall and younger sister, Tish.