Ex vivo platelet retention by albuminated glass and polystyrene beads has been evaluated as a function of flow rate, bead surface area, blood exposure time and albumin treatment. The stability of the albumin coatings as well as scanning electron microscopy of the various surfaces before and after blood exposure has also been included. Results indicate that platelet retention is sensitive to changes in the above parameters and that albumin pretreatment of different substrates can decrease platelet retention. This decrease is substrate dependent in that platelet retention is different for the albuminated glass and polystyrene substrates. Chemical analysis of the substrate materials by X-ray photoelectron spectroscopy (XPS) as well as bulk chemical analysis is also reported.