The flotation separation of sulphide minerals is achieved by controlling particle hydrophobicity, which is often described in terms of the liquid-vapour contact angle determined from wettability studies on single surfaces. These may not be representative of the true hydrophobicity of mineral particles in a pulp and there is a requirement to determine ＇＇particle contact angles＇＇. We report an experimental approach, based on equilibrium capillary pressure measurements across a packed bed of particles, which reliably and routinely determines the powder contact angle of mineral particles in the size range 10 to 200 mu m. The influence of particle size and surface treatment on the powder contact angle and flotation response of galena particles are reported. The natural hydrophobic nature of galena was shown to depend on the hydrodynamic conditions during particle conditioning. The high shear environment experienced during cyclosizing resulted in galena particles of greater hydrophobicity than those prepared by sieving. A mechanism is proposed to explain the relationship between hydrodynamic conditions, surface chemistry and hydrophobicity; this may give insight into the role of high intensity conditioning and sonication in sulphide mineral flotation. The correlation between collector coverage, particle wettability and flotation recovery was also investigated. Ethyl xanthate at surface coverages in excess of 0.1 equivalent monolayers significantly increased the particle contact angle and particle floatability. The influence of other reagents on galena particle contact angles is discussed.