The ultrastructure of regenerated optic fiber terminals differs from normal terminals during the first 12 months following optic nerve crush. The area of the regenerated terminals occupied by axoplasm initially increases (1 month postcrush, mpc), then declines to a below normal level (8-12 mpc) and eventually returns to the normal level (16 mpc). The density of vesicles within the regenerated terminals remains initially the same (1 mpc), then increases (4-12 mpc) and finally returns to normal values by 16 mpc. The multiplicity of reestablished retino-tectal synapses gradually increased from an initially lower value at 1 mpc to the normal value by 4 mpc whereas the length of their synaptic contacts decreased from an initial elongation (1 mpc) to the normal length (4 mpc).