Competitive protein adsorption from human serum onto unmodified polyethylene terephthalate (PET) surfaces and plasma-polymerized PET surfaces, using the monomer diethylene glycol vinyl ether (DEGVE), has been investigated using radioactive labeling. Albumin and immunoglobulin G (IgG) labeled with two different iodine isotopes have been added to human serum solutions of different concentrations, and adsorption has been performed using adsorption times from approximately 5s to 24 It. DEGVE surfaces showed indications of being nonfouling regarding albumin and IgG adsorption during competitive protein adsorption from diluted human serum solutions with relatively low protein concentrations, but the nonfouling character was weakened when less diluted human serum solutions with higher protein concentrations were used. The observed adsorption trend is independent of adsorption time, indicating that the protein concentration has a stronger influence on observed adsorption characteristics of the material than the adsorption time has.