Disclosed herein is a device for sampling blood by capillarity for separating a plasma phase of the blood from the cell phase. The device is a strip and includes a filter having a membrane with no clumping agents, a prefilter for spreading blood over the surface of the membrane and an absorbent paper downstream from the filter. The membrane is dimensioned to cover only a part of the surface of the prefilter and the migration of blood by capillarity within the prefilter takes place essentially lengthwise relative to the strip before blood comes into contact with the membrane.
