Previous research has shown that caffeine increases alertness and improves sustained attention. In contrast to this, consumption of lunch leads to a decline in the ability to maintain attention. The main aim of the present study was to determine whether caffeine removes or reduces the postlunch drop in performance, an issue which is of considerable practical importance and theoretical interest. The results showed that caffeine improved performance on the Bakan vigilance task and removed the post-lunch dip observed in the decaffeinated condition. Similar effects were observed in one of the conditions of a mental rotation task. The lunch X caffeine interaction observed in the Bakan task did not change over the course of the task. In contrast to the performance data, lunch X caffeine interactions were not observed in analyses of cardiovascular function or subjective mood.