A technique is presented to measure the flexural modulus of free-standing thin metallic films from 1 to 25-mu-m thick. Lamb waves are excited in the film with a pulsed Nd:YAG laser, and detected using heterodyne interferometry. Variability in wave-form structure is observed as a function of experimental parameters and film thickness. The first arrival of the symmetric Lamb mode can be unambiguously identified regardless of wave-form shape, and is used to calculate the flexural modulus.