Polycrystalline diamond films with a thickness of about 4 mu m were deposited with the hot-filament technique using methane concentrations between 0.5 and 2.0% in the source gas. Surface acoustic wave spectroscopy (SAWS) was employed to determine the density, Young's modulus (elastic or E modulus), and Poisson's ratio from the dispersion of propagating surface wave pulses. With decreasing CH4 concentration in the deposition gas, the density increased from 3.4 g cm(-3) to 3.5 g cm(-3) while the Young's modulus increased from 925 GPa to 1080 GPa. showing the improved mechanical and elastic properties for low methane concentrations. These results are correlated to those of other characterization methods such as Raman spectroscopy, scanning electron microscopy (SEM I), and atomic force microscopy (AFM).