To determine whether apoptosis is involved in retinal degeneration induced by intravitreal implantation of 5 iron particles in rat eyes. Autoclaved iron particles were implanted in the vitreous cavities of the experimental eyes. Glass chips were implanted in the control eyes. The experimental eyes were enucleated at various time intervals from days 1 to 15. Retinal degeneration was examined using the TdT-mediated, dUTP-biotin nick-end labeling (TUNEL) method. Electrophoresis on agarose gel was used to detect internucleosomal DNA fragmentation. TUNEL-positive nuclei were observed only in the outer nuclear layer beginning on day 2. The nuclei spread throughout the outer nuclear layer by the end of day 3. No TUNEL-positive nuclei were observed in other layers throughout the experimental period. Analysis of DNA, extracted from the retinas by electrophoresis on agarose gel, revealed a typical ladder pattern of internucleosomal DNA cleavage in the experimental eyes. Apoptosis occurred during photoreceptor cell death at the early phase of iron-induced retinopathy in these rats. Like photic injury, iron-induced apoptosis was limited to the outer nuclear layer.