The HSE spent over 1.1 billion euro on agency staff in less than two years.
According to freedom of information figures, almost a quarter was spent on nurses.
68 million euro was spent on agency staff in 2021, and 543 million in the first 11 months of last year.
Across the 23 months, almost 240 million was spent on nursing staff, 200 million on management and administrative staff, and over 101 million on paramedics.
The HSE says the availability of health staff continues to be a challenge, not only in Ireland but around the world.
Where there are shortfalls, agency staff are employed.
The HSE says in a number of instances in recent times, it has been unable to fill a vacancy, even with agency staff.