The frequency characteristics of the suppression by contralateral stimulations, of the cubic 2f1-f2 distortion products (DPOAEs), were studied during 63 sessions performed in 39 humans with normal hearing. Each session consisted of exposure to five successive series of randomized contralateral NBN frequencies centered between 0.25 and 8 kHz, while measuring 2f1-f2 set at one of the four studied frequencies, i.e., 1, 2, 3 or 5 kHz. For each value of 2f1-f2, analysis of variance and Student's t-test were used in order to indicate and, if necessary, to localize, a possible significant frequency specificity. Results showed that the suppression exerted on 2f1-f2 DPOAEs by contralateral sound stimulation, is frequency specific, at least for middle frequencies of 1 and 2 kHz. The frequency specificity is specially marked when 2f1-f2 = 1 kHz with contralateral NBN central frequencies around 1 kHz. When 2f1-f2 = 2 kHz, central frequencies which induced a significant suppressive effect include frequencies around 2 kHz and also lower frequencies around 1 kHz. These observations support the interpretation that the suppression of the DPOAE is mediated by the medial olivo-cochlear efferent system.