Optical techniques using voltage-sensitive dyes were used to record electrical events simultaneously from many positions on certain neurons of the barnacle supraesophageal ganglion. By signal-averaging, recordings with good signal-to-noise ratios and time resolution were obtained from fine dendritic processes as well as the axon and cell body. Controls established that the optical signals faithfully matched recordings made with intracellular electrodes for short times (5 to 10 msec), but deviations were observed at longer times. Pharmacological effects and photodynamic damage due to the dye were insignificant. The optical records were correlated with positions on the stimulated cell determined from Lucifer Yellow injections. This comparison demonstrated that signal-averaged records with large signal-to-noise ratios were obtained from those parts of the visual field which contained elements of the stimulated cell and hence could be attributed to specific locations on the cell. The quality of the optical signals were adequate to: (a) determine variations in the shape of action potentials in different parts of the cell; (b) demonstrate electrotonic spread of hyperpolarizing pulses; (c) determine the direction and velocity of action potential propagation, and (d) in some circumstances, using reasonable assumptions, estimate variations in the amplitude of action potentials or electrotonic pulses in different regions of the cell.