Abstract: An hourglass shaped blood fractionation tube is sized and shaped such that whole blood that has been centrifuged with a density gradient medium yields a PBNC layer within the narrowed neck of the tube. This orientation results in an elongated or widened PBMC layer, versus what would result in a conventional fractionation tube. Elongating or widening the PBMC layer allows technicians to harvest higher purity and higher volume PBMC samples versus samples harvested with a standard cylindrical blood fractionation tube. The hourglass shaped blood fractionation tube according to the present invention preferably includes a cap and can be used in conventional centrifuges and robotic pipetting stations.