An ipsilateral retinotectal projection was induced by ablating one tectal lobe. Radioautography indicated that the ipsilateral that the ipsilateral projection initially spread out continuously over the remaining tectal lobe. With time, the continuous projection progressively changed into a rostrocaudally oriented banded projection that was comprised of high and low silver grain density bands. The undamaged native projection from the contralateral eye also became transformed into high and low density bands. The results indicate that foreign fibers displace portions of the native projection. Complete segregation of the two projections was not found at any time point examined. Low density bands did not represent spillover of label from a high density band since cobalt-filled optic fibers were found in low density bands. Quantitative analysis indicated that the contralateral projection occupied more tectal area than the ipsilateral projection. Area occupied by a projection, band width and band frequency showed appreciable between-fish variability. Correlations between band width and per cent of area occupied by a projection approached unity, indicating that large projections were isolated with wider bands. A model is proposed to account for induced banding in lower vertebrates.