This experiment was conducted to examine the influence of a moderate dose of caffeine (4 mg/kg) on delayed memory, metamemory, and sustained attention. One hundred and forty-two volunteers ingested either caffeine or placebo during a study session which included three different memory tasks (free recall, cued recall, and recognition), and they made predictions of future memory performance. On day 2, participants again ingested either caffeine or placebo and completed memory tests. Sustained attention performance was measured on both days, and caffeine reliably improved hit rates and response latencies. A reliable drug-state interaction was detected only in the free recall test of memory. Caffeine did not affect the magnitude or accuracy of memory predictions, but there was some evidence that expectancies about caffeine were related to cognitive performance. Overall, caffeine's impact on memory and metamemory was not robust in this study. Copyright 2001 John Wiley & Sons, Ltd.