1. The spontaneous rhythmical impedance changes that occur in fertilized and unfertilized eggs of the rainbow trout after about 7 hr. immersion in tap water have been analysed. They are found to be almost entirely capacitative and correspond to a change of between 5 and 10 % when measured at a frequency of about 1.0 kc. The possibility of any associated resistance change being virtually unobservable is discussed.
2. These changes, which have not so far been recorded in other living material, are compared with the impedance changes that occur in nerve cells and Nitella.