A search for a male walker, on Mweelrea mountain in Co Mayo, has been called off for the night.
The man, who is in his mid-30s, has not been seen since last night.
He was reported missing to the gardai by his wife this afternoon.
It is understood the man is from the east of the country.
The search, by members of Mayo Mountain Rescue, will resume at first light tomorrow.
A Coast Guard helicopter was also involved in the operation earlier, but has now returned to base.