Following induction of long-term potentiation in subfield CA1 of the hippocampal slice from 26-month-old rats, shaft synapse numbers increased by 44% and sessile spine synapses (synapses on stubby, headless spines) by 72%, with the more common mushroom-shaped spine synapses statistically unaltered. These effects are smaller than in prior work with young adults, whereas population spike amplitude changes were comparable to young adults. Reasons for the discrepancy are unclear, but the results confirm continuing capacity for induction of LTP in aged rats and indicate that substantial synaptogenic capacity also persists, but may be impaired, at these ages.