The intensity of the chemiluminescence (CL) signal from an aqueous peroxyoxalate CL reaction can be significantly enhanced in the presence of various proteins with hydrophobic sites. A flow-injection measurement for various hydrophobic proteins based on this CL enhancement was developed. The enhancement is due to the inclusion of the CL species in the favorable environment provided by the protein's hydrophobicity, which results in efficient light production. Various protein structures were evaluated; the degree of enhancement depends on the protein structure and CL reaction conditions. The CL enhancement measurement in the flow-injection system is made after the introduction of the protein solution to the main phosphate buffer stream followed by the addition of the CL reagent streams: (1) hydrogen peroxide in water and (2) 8-anilino-1-naphthalene sulfonic acid and 4,4'-oxalylbis-(trifluoromethylsulfonylimino)ethylene bis(4-methyl morpholinium trifluoromethane sulfonate) in acetonitrile. Although prior separation of proteins is required before the measurement, the advantage of this approach is increased sensitivity without derivatization of the protein. The enhancement was demonstrated for several proteins, including antibodies, which suggests that this approach may be generally applicable to a variety of measurements, including immunoassay determinations. This CL enhancement was used to develop a simple and accurate flow-injection measurement for the determination of albumin and IgG in human serum.