This protocol includes the step-by-step protocol used to isolate human peripheral blood mononuclear cells (PBMCs) from fresh human whole peripheral blood using the Ficoll density gradient method. This method seperated cells based on sedimentation velocity and cellular density. Under centrifugal force, cells with a higher density compared to Ficoll-plaque (such as RBC and granulocytes) pass through the Ficoll layer and sediment at the bottom of the tube.However, cells with a lower density are unable to penetarte the media. Cells will a very low density (such as platelets) remain in suspension, while cells with a density similar to that of ficoll ( such as PBMCs) collect at the ficoll interface.