The results of investigations to determine the effects of several metallurgical and acoustical variables on the ultrasonic signal strength using commercially available ultrasonic flaw detection equipment are reported. Applied to various metals used in aerospace structures and components, these investigations resulted in the separation and determination of important acoustical properties that were expected to indicate the cause for differences in the trans mission of ultrasonic energy in the various materials. A method was developed for applying correction factors to test blocks of one metal in order to estimate the size of defects in other metals. Beam collimation techniques were studied to determine optimum conditions for detecting defects and displaying them on both cathode ray image and C-Scan (plan view) facsimile paper recordings. Some investigations were also performed to separate and identify shear and surface (Rayleigh) waves.