Suppression of congenital nystagmus by eyelid closure was studied by electrooculography in four cases under various conditions in order to elucidate whether the suppression is caused by blocking of fixation or not. The nystagmus persisted in the light as well as in the dark provided that the eyes were kept open. Frenzel's glasses did not suppress the nystagmus except for one case in whom jerky nystagmus was attenuated. In the other cases, only voluntary lid closure suppressed the nystagmus. Passive lid closure while the patient attempted to keep eyes open did not suppress the nystagmus except in one case. Reflex eyelid closure by glabellar tap did not suppress the nystagmus in spite of the occurrence of Bell's phenomenon. Passive eyelid opening while the patient attempted to keep eyes closed, on the other hand, did not reproduce the nystagmus. The suppression of congenital nystagmus by lid closure, at least in some cases, seems to be related to the voluntary effort to keep eyes closed but not specifically to blocking of fixation.