As part of a larger investigation on freeze-thaw durability of masonry segmental retaining wall (SRW) units, specimens of various geometries were extensively evaluated for their resonant frequency prior to freeze-thaw exposure. These pretest trials were conducted to assess the applicability of the impact resonance method on these specimens, to identify factors affecting test result interpretation, and to obtain initial values for future comparison with values after freeze-thaw cycling. The importance of correctly identifying resonant frequencies corresponding to different modes of vibration of the specimen is highlighted, and methods to achieve this in the laboratory are discussed. The effects of specimen moisture content variations, temperature, and sampling parameters on resonant frequency are also presented.