Pure shear waves are harmonically excited in gas-liquid foam and their phase vs frequency relationships are measured. These relationships exhibit approximately linear dependences. The shear wave speed is calculated from these relationships using a mathematical model. The relationship between the shear wave speed and the shear modulus is used to estimate the latter. The overpressure in the foam bubbles is measured and the ratio of the shear modulus to the overpressure is found to be 0.76. This value is approximately two to three times higher than the values reported in the literature for static measurements. This discrepancy is attributed to the dynamic character of the wave propagation measurements. (C) 1994 Academic Press, Inc.