The biocompatibility of modified and urease-immobilized poly(ethyleneglycol dimethacrylate/2-hydroxyethylmetacrylate) [poly(EGDMA/HEMA)] microbeads was tested through blood compatibility tests. Twelve percent HEMA incorporated nonporous particles of 105-125 mum were used in the research. Hydroxyl groups on microbeads were chemically modified by following a three-step procedure that is composed of activation, spacer-arm incorporation (hexamethylene diamine) and, finally, glutaraldehyde bounding. Enzyme urease was immobilized on microbead surfaces, and adsorption of blood proteins in serum and plasma, blood coagulation time, and leukocyte and platelet adhesion were tested. Incubation of 1.5 cc of biological fluid with 100 mg of urease-immobilized poly(EGDMA/HEMA) microbeads at room temperature shows that protein adsorption on surfaces occurs, but protein content after treatment was in the range of healthy people. Adsorbed albumin and total globulin amounts per gram of microbeads is much greater than fibrinogen. Immobilization of urease reduced the protein adsorption and blood coagulation times compared with those of modified microbeads. Prothrombin time (PT) was not altered much, whereas poly(EGDMA/ HEMA) microbeads induced a significant increase of activated partial thromboplastin time (APTT). The platelet and leukocyte adhesion slightly increased with the modification of poly(EGDMA[HEMA) and decreased with the introduction of urease. When blood samples were treated with urease-immobilized microbeads, BUN values of patients were lowered to almost acceptable amounts. (C) 2002 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 64B: 13-18, 2003.