The colloidal stability of polyethylene particles in standard cell culture conditions to gain insight into the possibility of particle agglomeration was analyzed. The change in zeta potential (zp) of the particles when suspended in solutions of varying protein species and concentrations was measured. The two particle species were shown to have very similar size distributions by number with the majority of the particles within the phagocytosable range. The zp results show a moderately negative potential for bovine serum albumin (BSA) at low concentrations, becoming less negative with increasing concentration.