Brillouin scattering measurements carried out on a thin Ælm of $C_{70}$ deposited on a Si(1 0 0) substrate show modes at 4.8 and 25 GHz due to the surface Rayleigh wave and the bulk longitudinal acoustic mode, respectively, the corresponding modes for $C_{60}$ being found at 4.3 and 30 GHz. Based on the Brillouin data, the values of the bulk, shear and Young's moduli of $C_{70}$ are found to be 11.3, 3.2 and 8.7 GPa, respectively (the corresponding values for $C_{60}$ are 14.9, 4.7 and 12.7 GPa). Poisson's ratios for $C_{70}$ and $C_{60}$ are comparable, the values being 0.37 and 0.36, respectively.