We agree with the conclusions of a recent article in this journal [James, Neuropsychobiology 1994;30:124-125] that studies on the psychoactive effects of caffeine need to take into account the possibility that the results obtained might represent merely the reversal of deleterious effects of caffeine deprivation rather than an actual net benefit due to caffeine use. However, in a review of recent studies we find no unequivocal evidence of impaired psychomotor performance associated with caffeine withdrawal. This is in contrast to a clear deterioration of mood which occurs even after overnight caffeine deprivation. We concluded that current evidence points to true performance-enhancing effects of caffeine, although the extent of these and the conditions under which caffeine is most effective have yet to be fully determined. At the same time, the existence of significant detrimental effects of caffeine deprivation on psychomotor performance has not been ruled out.