Gardaí in Wexford have released a man they were questioning in connection with the disappearance of 19-year-old Fiona Sinnott in February 1998.
Three others arrested earlier today remain in custody.
The three, a man and two women, are being held at New Ross and Enniscorthy Garda Stations under Section 30 of the Offences Against the State Act.
Ms Sinnott was 19 and a mother of one when she disappeared. Her baby daughter was eleven months old when the teenager vanished at Ballyhitt, four miles southwest of Rosslare.
Fiona was not reported missing for a number of days.
At the time of her disappearance, she was looking forward to her baby's first birthday, and her sister Diane's 21st birthday later the same month.
Fiona's disappearance was one of six cases of women who disappeared in Leinster; the cases formed the Operation Trace garda initiative in 1998.
Gardaí are appealing to anyone who may have information in relation to the disappearance of Ms Sinnott to contact them at New Ross Garda Station on 051-426581.