Abstract: A method for purifying conventionally treated blood plasma to remove substantially all residual leukocytes while maintaining useful flow rates for medically useful amounts of plasma utilizes a disposable, heat-sterilizable filter employing one or more depth-type prefilters and at least one intermediate hydrophilic microporous membrane followed by at least one final hydrophilic microporous membrane having a smaller pore size than the intermediate membrane within a common housing. The purified plasma is preferably subjected to chemical treatment to destroy infectious agents such as hepatitis and HIV.