Abstract: An insert beaker for centrifuges for centrifuging blood, having a blood bag placed in the insert beaker in association with a positive displacement body that acts upon the insert beaker from outside, the blood bag communicating via connecting hoses with at least one other blood bag inside the centrifuge. The insert beaker (1) is made with two pivotable shell halves (2, 3) joined together, and retaining elements for the blood bag to be placed between the shell halves (2, 3) is disposed on the top of the shell halves (2, 3).