Apparatus and method of magnetic separation.

Apparatus for observing magnetically responsive microscopic entities suspended in that a fluid medium, comprising: a container having a transparent wall; if a chamber formed therein for containing the fluid medium; ferromagnetic capture structure supported on the interior surface of the transparent wall; and magnetic means for inducing an internal magnetic gradient in the vicinity of the ferromagnetic capture structure, whereby the magnetically responsive entities if immobilized along adjacent the capture structure wall; characterized in that the ferromagnetic capture structure comprises a plurality of ferromagnetic elements having a non-uniform spacing between adjacent elements.