- The adsorption of albumin and thrombin to insoluble modified polystyrene resins bearing sulphonate (PSSO3) and L-arginyl methyl ester groups (PAOM) was investigated in both purified and plasma systems. Radioiodinated proteins were used to follow adsorption in a 'minicolumn' experiment. Albumin adsorption was found to follow the Langmuir model and specific surface areas of the various resins were evaluated from plateau albumin adsorption data. The adsorption isotherms of thrombin both in buffer and in antithrombin III/fibrinogen-free plasma were also found to be Langmuir-like, and the quantities adsorbed at the isotherm plateaux are in the monolayer range. Analysis of the isotherms at 4 degrees and 37 degrees C for the purified system shows that adsorption is endothermic. Adsorption capacities in plasma remain high (30-50% of those in the purified system) despite competition from the other plasma proteins. These data confirm the strong affinity and selectivity of these resins for thrombin.