This S100 EIA is a solidphase, twostep, noncompetitive immunoassay based on two mouse monoclonal antibodies specific for two different epitopes expressed in S100B. The assay determines both S100A1B and S100BB without crossreactivity with other forms of S100. Calibrators and samples are incubated together with biotinylated AntiS100B monoclonal antibody (MAb) S23 in Streptavidin coated microstrips. S100B present in calibrators or samples is adsorbed to the Streptavidin coated microwells by the biotinylated AntiS100B MAb during the incubation. The strips are then washed and incubated with horseradish peroxidase (HRP) labelled AntiS100B MAb S53. After washing, buffered Substrate/Chromogen reagent (hydrogen peroxide and 3, 3’, 5, 5’ tetramethylbenzidine) is added to each well and the enzyme reaction is allowed to proceed. During the enzyme reaction a blue colour will develop if antigen is present. The intensity of the colour is proportional to the amount of S100B present in the samples. The colour intensity is determined in a microplate spectrophotometer at 620 nm (or optionally at 405 nm after addition of Stop Solution). Calibration curves are constructed for each assay by plotting absorbance value versus the concentration for each calibrator. The S100B concentrations of samples are then read from the calibration curve.