The aim of this work is to investigate the relationship of interaction forces in the protein adsorption onto polymeric microspheres. In our previous study, the. relationship between predominated over hydrogen bonding, and when it was large, hydrogen bonding did. The transition point was observed when the two forces were exactly balanced. In this time, the relationship between hydrophobic and electrostatic interactions was investigated with the sulfonated microspheres. Just as the previous results showed, hydrophobic interaction governed the adsorption in the low sulfonated microspheres and electrostatic interaction did in tile high sulfonatcd ones. However, the transition point was shifted to the left. In case there existed only one interaction force, the adsorbed amount was in the following order : electrostatic > hydrogen bonding > hydrophobic.