During compression of the entire retinotectal projection into the rostral half of the tectum after ablation of the caudal half there is widespread sprouting of ganglion cell axons, not only those cut during the operation but also those left intact. However, unlike cut axons those left intact sprout without their cell bodies showing chromatolysis or swelling. Chromatolysis and swelling of the cell bodies of cut axons are more prolonged than after optic nerve section and resolve in more central regions of retina first. The cut axons of cell bodies in these regions tend to be the first to form terminal arborizations during the compression process as judged electrophysiologically. However, there is no clear correlation in individual fish between these measures and the state of compression assessed electrophysiologically. Large areas of retina may contain chromatolysed cells even after compression has occurred. Electrophysiological mapping alone may give a misleading picture of the interactions occurring between retinal and tectal cells during reorganization.