The tensile strength of a powder bed of calcium carbonate moistened with aqueous solutions of surface-active agents was measured in air and in carbon tetrachloride by a diametrical compression method. The cohesive force at the point of contact of particles was determined by means of the Rumpf equation. The cohesive force determined by the diametrical compression method was much stronger than that obtained by the traction table method in air. This finding suggests that the area of contact played an important role in determining the cohesive force. When the liquid saturation ratio was less than 20%, i.e. in the pendular region, the cohesive force increased with increasing saturation ratio in both air and liquid. The cohesive force also depended on the interfacial tension of the moistening liquid, the action of which was slightly different in liquid and in air. The cohesive force was drastically decreased by rendering the particles hydrophobic. It is suggested that the cohesive force at the point of contact in the pendular region can be represented qualitatively by equation (7) in the text. H=ψf (γ) f (S) f (θ, β) (7) In the funicular region, where the liquid saturation ratio was larger than 20%, the cohesive force decreased with increasing saturation ratio. This might be due to the action of agglomerates formed in the powder bed. It was also found that the cohesive force increased with increasing interfacial tension of the moistening liquid.