The overall objectives of the proposed research is to gain an understanding concerning the ionic mechanisms of the retinal cell potentials that play an indispensable role in the information processing in the retina. An analysis of the potentials in each neuron is also necessary for a better understanding of transretinal potentials which are of particular value in the diagnosis of retinal diseases. The slow retinal cell potentials are the electrical manifestation of synaptic mechanisms. In order to simplify the synaptic inputs and make the analysis easier, the synaptic interaction between two neurons is studied by stimulating individual neurons by current through the recording electrode while recording responses of two neurons simultaneously by two independent electrodes. Individual neurons are also stimulated chemically by local application of chemicals near the synaptic site. These methods are combined with the stimulation of population of neurons by light and by transretinal current. The responses of bipolar, horizontal, amacrine and ganglion cells are recorded intracellularly and their response properties are analysed by electrophysiological methods. The routine methods include the measurement of spectral responses, of changes in the input resistance, and of reversal potentials by passing polarizing current through the intracellular electrode. With regard to the ionic mechanisms of horizontal cell responses, direct measurements are made of intracellular Na ion, K ion and Cl ion with ion-specific microelectrodes, utilizing the huge horizontal cells of the stingray.