Ellipsometry and total internal reflection fluorescence spectroscopy(TIRF) were used for investigating adsorption processes of relevance forparenteral administration of colloidal drug carriers. Emphasis is put ondiscussing the effects of both protein and surface properties on theadsorption of serum proteins at phospholipid and other surfaces.Furthermore, the adsorption from multicomponent protein systems, such asblood, is addressed, and both competitive and associative adsorptionphenomena discussed. The correlation between effects of the drug carriersurface properties on the serum protein adsorption and the circulation timeand tissue distribution of colloidal drug carriers is also addressed.Finally, the potential of ellipsometry in another adsorption process ofmajor importance for phagocytosis, i.e., the adsorption of colloidalparticles to macroscopic or mesoscopic surfaces, is indicated byinvestigations of the adsorption of oil-in-water emulsion droplets atsilica.