We report the catalytic properties of plasmin irreversibly adsorbed to surfaces made of a mixture of graphite carbon with nujol (graphite carbon paste). The assay of the immobilized enzyme was achieved, under forced convection, with a specific and chromogenic substrate (S-2251) dissolved in the solution, under varying temperatures and pH conditions. Results showed that these two variables affected more critically the activity of the adsorbed enzyme than that of the free form. Also differences observed in the respective activity vs pH relationships suggested that the coated surface was able to discriminate between different isoelectric forms of plasmin. Time-varying activities observed in the temperature range 10-30-degrees-C were interpretated in terms of the first-ordered thermal denaturation reaction, which affected some of the adsorbed plasmin forms.