Abstract: A method and device are provided for separating magnetized particles from biological fluids. Cells such as cancer cells coated with magnetized particles can be separated from uncoated healthy cells. A fluid mixture of cancer cells, healthy cells and magnetizable particles is introduced into a container such as a disposable blood bag which is attached in a cassette on an underlying plane magnetic plane that provides a magnetic field. Incubation is carried out during which the cancer cells become coated with the magnetizable particles. The magnetic field pulls the coated cells down towards the bottom of the bag and anchors them, and uncoated healthy cells are removed from the bag. The separated uncoated healthy cells may be advanced through a final separation unit where any loose magnetizable particles are removed. There is provided means for adjusting vertical distance between the cassette and the magnetic plane and for agitating fluid within the container attached to the cassette.