The effect of piracetam on visual event-related potentials (ERP) was investigated in a double-blind placebo-controlled study. Eight- to 12-year-old dyslexic males were randomly assigned to 3.3 g/day of piracetam or matching placebo in two divided doses over a 12-week period. Children performed a vigilance task in which they pressed a key when two alphabetic letters or shapes occurred in sequence. ERPs to letters and shapes, for active and passive responses, were recorded at the vertex and left and right parietal areas of the scalp. Performance measures included letter- and form-hits, misses, commission errors and reaction times. Piracetam increased the amplitude of a late positive component (believed to correspond to P300) at the vertex for letter-hits. Piracetam also increased the latency of this component in both hemispheres, but only for active responses (letter-hits) in the left hemisphere and passive responses (correct rejections and misses) in the right hemisphere. Although piracetam did not significantly affect performance, reaction time to letter-hits was significantly correlated with the latency of the P300 component, suggesting that letters created increased effort or attentional demand on the subjects compared with forms. An early ERP component (P225) also showed increased amplitude to piracetam in both hemispheres and effects were limited to form-hits. These effects were thought to possibly reflect slow negative potentials arising from stimulus anticipation in the CNV-like paradigm. In view of the small sample size, the results were cautiously interpreted as indicating a facilitation of verbal processing mechanisms responsible for analyzing the verbal significance of visual stimuli.