The ultrastructural features of hippocampal synaptic contact zones have been investigated by means of computer-assisted morphometry in rats of 6, 12 and 22 months of age and in age-matched animals chronically treated with ALCAR at a daily dose of 50 mg/100 g body weight from the age of 1 month up to the day of sacrifice. The number of synapses/microns 3 (Nv), the average size of the junctional areas (S) and the total area of the synaptic contact zones/microns 3 (Sv) were measured in tissue samples stained by means of the ethanol phosphotungstic acid (E-PTA) preferential technique for synaptic membranes. In control animals Nv was constant between 6 and 12 months of age, but significantly decreased in 22-month-old rats; S did not show significant differences due to age; Sv was unchanged between 6 and 12 months, but it decreased significantly in the old animals. In ALCAR treated rats Nv increased and S decreased significantly vs. Age-matched controls. Sv showed a lifespan constancy among the groups of age analysed. In ALCAR treated rats the number of contact areas smaller than 0.08 micron 2 increased by 18, 9 and 10% at 6, 12 and 22 months of age, respectively. ALCAR administration resulted in a lifespan modulation of synaptic structural dynamics. A proper metabolism at nerve terminals is accounted to play a crucial role in synaptic remodelling potential: on the basis of current research data, it is suggested that ALCAR may improve neuronal bioenergetic mechanisms.