THE retrograde nucleophilic tracer diamidino yellow (DY) was injected into the left superior colliculi of 2-day-old rats. Two days later, right eyes were injected with either neurotrophin NT-4/5, cycloheximide (CHX), MK-801 and DNQX (glutamate receptor antagonists), or saline. Almost all rats were perfused 6-7 h later and the numbers of normal and pyknotic DY-labelled retinal ganglion cells (RGCs) were determined from retinal whole mounts. In controls (no eye injection) the proportion of pyknotic RGCs was 1.04%. This level of naturally occurring death was significantly reduced after injection of NT-4/5 (0.34%); normal RGC density was also higher in this group. RGC pyknosis was increased after saline (1.21%), MK-801/DNQX (1.22%) or CHX (1.48%) injections but only in the latter case was the increase significantly greater than control.