The cell biology of sperm-egg interaction will be examined in the sea urchin egg, especially with respect to the process whereby excitation of the egg resulting from sperm attachment leads to activation. The nature of the signals exerted at the surface which initiate excitation of the egg (sperm-ligand egg-receptor interaction and/or fusion of the sperm and egg membranes) will be examined. The nature of the signals transmitted from the surface which initiate activation will be investigated. The evidence up to the present indicate that these signals involve the turning on and off of specific ion fluxes. These will be meaasured as currents recorded from voltage clamped eggs following sperm attachment. A combination of atomic absorption, electron microscopic, and electrophysiological methods (membrane potential, resistance, and capacitance measurements, current and voltage clamp analysis, and patch clamp techniques) will be used.