OBJECTIVES: 1) A study of the metabolic and ionic dependences of photoreceptor cell currents and electrical potentials in darkness and in light. 2) A study utilizing intracellular recordings from photoreceptor cells for relating intracellular potential and membrane conductance with respect to the effects of changes in metabolic activity and ionic concentration gradients. 3) A study to define more precisely the rates and controls of metabolism in relation to the generation of electrical activity in the photoreceptor cell by measuring lactic acid production and glucose oxidation.