The search for Maura Reynolds, missing from a nursing home in Bray in Co Wicklow, is expected to resume in the morning.
Today's search was concentrated in the sea around Bray Head.
Members of the Garda Underwater Unit, the coastguard and Bray Sailing Club took part.
Mrs Reynolds, 78, suffers from Alzheimer's and a form of cancer.
She was last seen at the Tara Nursing Home in the early hours of Monday morning.
She had returned there earlier that evening following a visit to her family.
