A 25-year-old man from the southside of Limerick city remains in a critical condition in hospital after he became unwell over the weekend.
The man was one of five members of the same extended family who presented themselves at the Mid-Western Regional Hospital in the early hours of Monday morning.
It is believed the five relatives, who each displayed similar symptoms, had attended a party on the southside of the city late on Sunday night.
The men, who are aged in their late teens and 20s, were treated at the hospital and three of them were discharged by doctors on Monday afternoon.
However, two of the men required further treatment and one of them remains in the intensive care unit where its understood his condition has improved slightly today.
Gardai have confirmed they are investigating the circumstances of how the men became unwell and they are looking to establish if illegal drugs were a factor.
A number of searches were carried out at the mens homes yesterday afternoon as part of the investigation.
Gardai at Roxboro Road are appealing for information and can be contacted at (061) 214340.