Blood washing method using a saline wash solution of varying concentration for use with blood washing apparatus

In a method of washing blood by providing blood in a rotatable enclosure member and thereafter introducing saline wash solution into said rotatable enclosure member to contact said blood for a pre-determined washing period and thereby remove contaminants therefrom the improvement which comprises decreasing the concentration of the introduced saline solution from an initial relatively high concentration to a predetermined lower concentration at a substantially linear rate while maintaining the flow rate of the saline solution at a constant value throughout the washing period.