Acetyl-l-carnitine (ALC), a natural component of several biological systems, has been found to modify spontaneous and evoked electrocortical activity in young rats and to improve learning ability in old ones. In clinical application it also improves mood and attention in elderly patients. The present study was aimed at ascertaining the effect of a chronic treatment with ALC added to drinking water on two discrimination models in aged rats. In the first model, simple discrimination learning was tested and was found to be significantly improved by treatment. The second model consisted of a differential reinforcement of low rate of responding. The animals receiving treatment performed significantly better as shown by a lower number of nonrewarded responses. Because impaired learning and memory are related to alterations in hippocampal function, these data indicate that ALC is capable of antagonizing the natural age-dependent deterioration process in the hippocampal structure.