Method for removing leukocytes

A method for removing leukocytes from a leukocyte-containing suspension, comprising the steps of:

• passsing a leukocyte-containing suspension through a filter unit which comprises:
• a container having at least one inlet conduit means and at least one outlet conduit means;
• and
• a main filter packed therein in the form of a non-woven fabric, said fabric comprising fibers wherein the average diameter of all of the fibers in said fabric is from 0.3 .mu.m to less than 3 .mu.m and said fabric having a bulk density of from 0.01 g/cm.sup.3 to 0.7 g/cm.sup.3, and wherein the average distance between any two of all adjacent fibers throughout said fabric is 0.5 .mu.m to 7.0 .mu.m and is defined by the following equation (1):
• ##EQU5## wherein y is the average distance between two adjacent fibers in microns;
• x is the average diameter of fibers in microns;
• .rho. is the density of the fibers in g/cm.sup.3 ;
• D is the bulk density of the filter in g/cm.sup.3 ;
• and .pi. is a circular constant;
• separating out storage generated microaggregates and adhesive substance with a prefilter inserted in the container between the inlet conduit means and the main filter;
• and obtaining a leukocyte-poor liquid.