Memory for a list of 20 words can be enhanced by preceding learning by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution (Psychopharmacology 137 (1998) 259; Psychopharmacology 157 (2001) 46). However, using this anterograde administration procedure, it is impossible to separate whether glucose affects encoding, consolidation, or retrieval. The present placebo-controlled, double-blind study investigated the effect of anterograde and retrograde administration on memory performance in healthy young participants. In order to evaluate whether post-acquisition administration of glucose can improve memory performance and to compare possible differences in the size of the effect, participants were administered 25 g of glucose immediately before or immediately after presentation of a word list. Moreover, in order to investigate whether the effect of glucose administration on memory performance is time-dependant, a third group received 25 g of glucose 15 min before learning the word list. Word- list recall was tested 30 min and 24 h after word list presentation. Measures of spatial memory performance and working memory were also evaluated. The results of this study showed that both pre- and post-acquisition oral glucose administration (25 g) can improve memory performance. However, as the time interval between anterograde glucose administration and memory encoding increased, the glucose memory facilitation effect decreased. This study provides evidence that glucose enhances memory performance in healthy young people even when it is given after learning has taken place, and that this effect is observed at least up to 24 h after glucose administration. Moreover, it provides evidence that the effect of glucose on memory performance may be time-dependent, as the enhancement of retention was decreased when the administration-learning interval was increased.