The search for alternate sources of energy has prompted interest in small ceramic beads, called “proppants,” which were developed as a means of “propping” open cracks during the hydraulic fracturing of bedrock in the vicinity of oil wells; recently, they have been considered as possible thermal transfer media for use in solar receivers [J. R. Hellmannet al., “Evaluation of Spherical Ceramic Particles for Solar Thermal Transfer Media,” SAND86‐0981, Sandia National Laboratories, January 1987]. To monitor the effects of repeated thermal stresses on the proppants, one would like to have a reliable measure of their elastic constants; however, their spherical shape and small size (≃ 500 μm) make conventional techniques, such as pulse‐echo, inapplicable. Using a special piezoelectric film transducer and a small‐sample resonance technique [J. D. Maynard, J. Acoust. Soc. Am. Suppl. 185, S20 (1989)], the authors have been able to determine the elastic constants and their variation as a function of heat treatment. [Work supported by the Office of Naval Research and NSF Grant DMR 9000549.]