Abstract: Derivatization of soda-lime glass spheres with aminosilanes and the stability of these groups at near-physiological pH in flow streams of aqueous buffered solution were studied. The extent of silanization was determined by a radioactive tracer method and a method based on a fluorescent marker, which confirmed the presence of immobilized and adsorbed amines in the nmol range. A method for covalently attaching bovine serum albumin to the beads via a cross-linking reagent which reacts selectively with amines is described. Thermal pre-treatment of the glass before derivatization enhanced suface derivatization with aminosilanes. Less than monolayer films prepared with monofunctional silanes were stable, after initial conditioning, with a 3% loss over 24 h in constantly flowing solution at pH 8, allowing the design of reusable immunoassay systems which were readily calibrated.