The objective of this study was to investigate the effects of organic materials used as coupling agents in acoustic analyses of biological materials. Ultrasonic wave propagation velocity was tested in steel with the application of coupling agents frequently applied in industry: Sonagel W, ŁT machine lubricant, 4W-40 motor oil and wallpaper adhesive. Ultrasonic wave propagation velocity is generally known, therefore, it was treated as a standard value. Ultrasound velocity was then determined for steel using the following organic materials as coupling agents: mains water, distilled water, liquid honey, crystallised honey, butter and vegetable oil. The evaluation criterion was the thickness of natural layer formed at the contact point between the head and the tested material which influenced measurement results, and the substances used in industry, in particular Sonagel W, liquid honey and butter were found to be such substances.