ABSTRACTNanoparticles (NP) are introduced in a growing number of commercial products, including food and beverage, daily use hygiene products such as toothpaste, or orally-administered drugs. To study the possible toxicity of these nanoparticles, a model system is the in vitro response of eukaryotic cells to the presence of NP. However, to understand the observed effects, it is clear that good physical and chemical characterization of NP, and in particular of their dispersion are needed. Indeed, the expected effects should be different if the study is dealing with agglomerates or isolated nanoparticles. For fundamental understanding, it appears important to work with nanoparticles as well dispersed as possible while being in relevant biological condition, i.e. cellular culture cell.In this context, we have studied the dispersion of a very common industrial titania NP (Degussa P25 produced in ton quantities). When dispersed in water, the suspensions of NP appear stable for weeks.. When transferred in the cell culture medium (DMEM) or if directly dispersed in DMEM, strong evolution of size is seen as well as sedimentation. To address this problem, we have compared different ways, coming from materials science, of dispersing NP in water with the idea to break in a preliminary step some of the necks between nanoparticles. The effect of dry ball milling, liquid ball milling, size of the balls and Ultrasonic dispersion will be compared. The best results were obtained from high power ultrasonic dispersion. To avoid direct aggregation, when going to DMEM, a “surfactant” relevant with biological studies (Foetal Bovine Serum (FBS)) was added in the suspension in order to coat the nanoparticles prior to transfer in DMEM (or other cell media). The result obtained with various surfactants and cell media will be presented. It must be noted that our best results were obtained in the FBS + DMEM medium.