People are being encouraged to roll up their sleeves and give blood.
Donor sessions will be held in July in Potters Bar and Barnet on Saturday.
Queen Elizabeth Girls School, in Meadway, Barnet, will hold a session from 9.30am to 4.15pm.
In Potters Bar, a session at the Wyllotts Centre, in Darkes Lane, from 1pm to 7.30pm.
For more information call 0300 123 23 23.