Recently numerous reports of electrocochleography performed in endolymphatic hydrops suggest that abnormal electrocochleographic potentials can be specific for this disease. Most authors described the following changes : (1) decrease and distortion of cochlear microphonics(Brookes et al, 1982), (2) increase of action potential thresholds(Schmidt, 1976 ; Kumagami et al, 1982), (3) steep increase of action potential amplitude with stimulus level(Kumagami et al, 1982), (4) increase of negative summating potential and abnormal AP-SP complex(Eggermont, 1976 ; Gibson et al, 1977 ; Coats, 1981 ; Goin et al, 1982 ; van Deelen et al, 1987). Authors induced an endolymphatic hydrops in the right ear of each of 30 albino guinea pigs by obliteration of the endolymphatic duct and sac. The AP and SP were picked up in the hypropic ears and in the control ears near the round window at 2, 3 or 4 weeks after obstruction of the endolymphatic duct and sac. The important findings obtained were : 1) Hydropic ears showed significant increase of AN1(first negative peak of AP) threshold. 2) In the low frequency range, the significant increase of AN1 amplitude and the significant prolongation of the AN1 latency were observed in the hydropic ears. 3) There were no significant effects of hydrops on SP amplitude or SP/AP ratio in these early groups. 4) In the high frequency range, AN2(second negative peak of AP) amplitudes were increased in the hydropic ears.