Protein adsorption at polymer surfaces has been investigated by means of both ELISA and radiolabeling techniques. Most of the data obtained are linearly related to each other for protein concentrations between 0.01 and 1 mu g/ml, i.e., the concentration range in which the maximum amount of adsorbed active protein (ELISA) is achieved. The correlation of ELISA data with radioisotope-based measurements allows quantification of the former. Specific correlation factors are described. Adsorption is shown to be strongly dependent an the polymer/protein system.