Ellipsometry and total internal reflection fluorescence spectroscopy (TIRF) were used for investigating adsorption processes of relevance for parenteral administration of colloidal drug carriers. Emphasis is put on discussing the effects of both protein and surface properties on the adsorption of serum proteins at phospholipid and other surfaces. Furthermore, the adsorption from multicomponent protein systems, such as blood, is addressed, and both competitive and associative adsorption phenomena discussed. The correlation between effects of the drug carrier surface properties on the serum protein adsorption and the circulation time and tissue distribution of colloidal drug carriers is also addressed. Finally, the potential of ellipsometry in another adsorption process of major importance for phagocytosis, i.e., the adsorption of colloidal particles to macroscopic or mesoscopic surfaces, is indicated by investigations of the adsorption of oil-in-water emulsion droplets at silica.