Binaural interaction is discussed by comparing the mon- and binaural speech audiograms. It appears to be possible to distinguish between two types of perceptive deafness. If the binaural speech audiogram is steeper (roughly by a factor 2) than the monaural curves, the deficiency is located anywhere between cochlea and superior olivary nucleus. If the binaural curve is parallel to the monaural one, the deficiency is located centrally beyond the superior olivary nucleus. Binaural interaction is further discussed from the point of view of supplementation. Binaural discrimination loss is reduced in almost half of the cases by a factor 1.9 as compared with monaural loss. The useful dynamic range is increased by 4 db on the average. The scattering of the binaural measurements is 0.79 times the monaural values. Recruitment-like phenomena are present in 64% of the cases with peripheral deafness in 34% of the central cases.