There is evidence that caffeine increases alertness and reduces fatigue. This may be especially so in low arousal situations (e.g. working at night or for prolonged hours). Caffeine has also been found to improve performance on vigilance tasks and simple tasks requiring sustained response. Again, these effects are often clearest when alertness is reduced, although there is evidence that benefits may still occur when the individual is unimpaired. Most studies to date have investigated the behavioural effects of caffeine in laboratory experiments using artificial tasks. In the current study 3 mg/kg caffeine was found to improve steering accuracy in a 1 h simulated drive. Measures of mood and performance on a sustained attention task also showed the benefits of caffeine. These findings suggest that laboratory results reflect a general benefit of caffeine that may also be observed in real-life situations. Other evidence examining the effects of caffeine on performance efficiency over the working day has shown the benefits of caffeine consumption on measures of sustained attention and alertness. This study also provided evidence suggesting that caffeine is often consumed when alertness is low to maximise alertness and performance efficiency. The implications of these findings for road safety are also considered. Copyright 2001 John Wiley & Sons, Ltd.