Surface forces in low-dielectric media are much less understood than those in aqueous solutions. In this work, the technique of colloidal-probe atomic force microscopy (AFM) was used to measure the force between a silica sphere and a flat silica plate in dodecane. A transient attractive force was measured, which slowly vanished during the first hour of measurements, following the characteristic dielectric relaxation time of dodecane. Subsequently, equilibrium conditions were reached. Equilibrium forces exhibited a strong dependence on the relative humidity of the environment. An attempt was made to explain the transient attractive force in terms of electrostatic interaction. (c) Koninklijke Brill NV, Leiden, 2008.