In medicine, the uses of nanoparticles (NP) offer new perspectives in imaging (Wagner, 2006), drug delivery (Salmaso, 2004) or radiotherapy (Hainfeld, 2004). However, questions about potential toxic and deleterious effects of nano-structured materials have been raised (Hoet, 2004; Maynard, 2006). Our objective is to develop standardized methods to assess NP toxicity on alveolar macrophages. However, the measurement of biomolecules released in the cell culture supernatants can be modified by their adsorption on the NP. Thus, this adsorption mechanism must be fully understood to avoid misinterpretation of data.