We investigated the relationship among the expression of single-stranded DNA (SSD) and double-stranded DNA (DSD) and the p53 tumor suppressor gene in delayed neuronal death (DND) of CA1 in the gerbil hippocampus after transient brain ischemia. Although SSD proteins appeared in CA1 pyramidal cells 1 day after ischemia, p53 immunopositive cells and TUNEL positive cells were not detected, and there was no statistical difference in the number of pyramidal cells compared with the control animals. A significant reduction (29%) in the number of surviving pyramidal cells was observed compared with the control animals at day 3 after ischemia. Also, expression of SSD, p53 immunopositive cells and TUNEL positive cells were detected. At day 7 after ischemia, the number of p53 immunopositive pyramidal cells decreased along with a decrease in the number of SSD- and TUNEL-positive cells. The percentage of surviving pyramidal neurons was reduced almost 83% compared with the control animals. It was considered that this early expression of SSD with transient ischemia was a character of DND. Expression of SSD may be a trigger for progression of the death cascade.