Health Minister Mary Harney has been pelted with red paint as work began on a new mental health unit.
The TD was splattered across her neck, hands and clothes as protesters angry at health budget cuts gathered at the planned facility in west Dublin.
Despite the paint attack, Ms Harney continued with the turning-of-the-sod ceremony at the new Ballyfermot Primary Care and Mental Health Centre.
The attack took place in the grounds of the unit as up to 20 protesters mounted a demonstration at the gates.
A Garda spokesman said a woman was arrested on suspicion of assault on Ms Harney in the grounds of Cherry Orchard Hospital.
The suspect was being detained in Ballyfermot Garda Station for questioning.