Amplitude differences between extraverts and introverts in the P300 component of visual event-related potentials were examined in a picture classification task. A set of pictorial stimuli was used with three types of instructions, requiring responses based on colour, semantic category, or a combination of both criteria. Forty university students (22 men, 18 women) served as subjects. Based on their scores on the Eysenck Personality Inventory, they were divided into 3 groups of Low, Medium or High Extraversion. The pictures evoked large late positivities, with higher amplitude in the right hemisphere. P300 amplitude increased with increasing degrees of extraversion. The effect of extraversion on amplitude (High > Medium > Low) was larger for target stimuli in posterior derivations. The extraversion effect was mainly attributable to the impulsivity subtrait. Whereas some earlier studies have found higher P300 amplitudes for introverts in tasks inducing habituation or attention decrement, the present tasks differed by using more varied stimuli and by requiring more processing. The results are discussed in relation to theories on the biological basis of extraversion.