We know a great number of methods for investigating the Physiology and Pathophysiology of the acoustic system, but seldom were several methods applied together to solve one single problem. In our own experiments we demonstrate the importance of correlated investigations on the acoustic system. They show, e.g., that functional impairment of the sensory cells in the organ of corti, caused by ototoxic drugs, can earlier be seen than morphological changes. The sensory cells with nuclear swelling are functionally inactive, and even those with morphologically normal appearance sometimes show functional impairment. A differentiation of damages caused either by acoustic stimulation or by ototoxic drugs is possible by electrophysiological and immunophoretical but not by morphological means. Therefore we think that the correlation between morphological, electrophysiological and biochemical findings gives us better information about the inner ear function.