The Irish Blood Transfusion Service has just five days worth of supplies left, and is calling for more donations.
It says bad weather and higher-than-expected demand from hospitals have led to the shortfall.
Operations director Paddy Bowler said a number of extra clinics were taking place around the country today to boost donations, with additional blood donation clinics in Westmeath, Cavan, Tipperary, Kildare and Cork. Details of the clinics are at giveblood.ie.
"Attendances at clinics have dropped significantly given the bad weather and the flooding," he said.
"The local advice in most cases has been not to travel unless absolutely necessary. At the same time, hospital demand was a little bit higher over the Christmas period."
You can see the current blood supply (as of January 15) here.
Don't know whether you can give blood? Find out here.