AbstractWe review recent work on the adsorption of proteins on two types of well-defined colloidal particles, namely on i) spherical polyelectrolytes that consist of a solid core onto which long chains of a polyelectrolyte are attached, and ii) core–shell microgels that have a shell of crosslinked poly(N-isopropylacrylamide) (pNiPAm) chains. The latter system may bear charges as well by copolymerization with acrylic acid. The surface layers of both systems that have a thickness of ca. 50 nm create a microenvironment in which the salt concentration and the pH differ from the outside solution. Adsorption of various proteins to these particles is monitored by various methods including calorimetry, fluorescence spectroscopy and small-angle X-ray scattering. These investigations also include studies of the kinetics of adsorption. The secondary structure of the proteins can be analyzed in these systems by FT-IR spectroscopy. Their tertiary structure can be checked by measurements of the enzymatic activity. In some cases the adsorbed enzymes exhibit an even higher activity as compared to the free protein in solution. We review the application of these techniques to monitor adsorption of proteins to these particles. All data demonstrate that both types of particles present model systems that help us to explore the main driving forces of protein adsorption.