The pattern of regenerating optic axons following various surgical manipulations in the goldfish brain has been studied using ('3)H proline radioauthography. The results demonstrate that in most cases severed optic axons regenerate preferentially into degenerating axonal pathways. It is therefore suggested that the degenerating axonal debris and the concomitant glial proliferation in a degenerating pathway, in some way, influences the entry of regenerating optic axons into the path. However, in view of the exceptional cases in which regenerating optic fibers either failed to grow into a degenerating pathway, or grew into pathways which apparently did not degenerate, it is further suggested that the influence of the degenerating pathways on the regenerating optic axons is neither 'compelling' nor 'restrictive'. Similarly, although the results also demonstrate that denervated optic terminal zones may influence the choice of pathways by regenerating axons and that the proximity of a pathway to the regenerating optic axons may do so as well, such influences are also neither 'compelling' nor 'restrictive'. Taken together, the data presented here indicate that the guidance of regenerating optic axons is probably influenced by a combination of these factors.

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