Abstract Electrokinetic properties of galena and chalcopyrite which exhibited collectorless flotation behaviour have been investigated using a microelectrophoresis technique. The isoelectric point (i.e.p.) of galena varied, depending on the method of sample preparation and pretreatment, from about pH 6.8 to pH 2.2. The latter has been shown to represent the i.e.p. value for a sulphur sample obtained from galena itself and also for chalcopyrite. In the acidic pH region, the zeta-potential values of an oxidized galena and the sulphur have been found to be remarkably similar, being represented essentially by the same curve. The results are in keeping with the previously reported studies on the influence of sulphur in rendering these minerals hydrophobic.