The friction between a single silica glass sphere and a flat silica glass surface has been investigated using lateral force microscopy. Two types of silica surface were investigated, one fully hydroxylated and the other partially dehydroxlated. These samples have markedly different wetting properties and are known as hydrophilic and hydrophobic silica, respectively. The lateral friction force as a function of applied normal load has been collected for five differentsized spheres for both surface types. Analysis of the friction versus load data indicates that the hydrophilic surfaces have a molecularly smooth contact. For the hydrophobic surfaces, it is not clear whether the friction-load response is caused by a smooth or an asperity-dominated contact zone. (C) 2000 Academic Press.