We investigated the processing of emotional stimuli during a non-sleep-deprived state and following sleep deprivation in 36 right-handed men. Using the visual half-field technique, cartoon line drawings of emotional facial expressions were flashed on a computer screen for 250 msec. The participants were instructed to remember the content of the picture seen and to recognize it among nine alternatives shown immediately after the display of a single picture. Compared to the nondeprived condition, response latencies increased and accuracy decreased in sleep deprivation. Moreover, response latencies indicated that the performance of the right hemisphere deteriorated more following sleep deprivation than did the performance of the left hemisphere. The results also showed that hemispheric preference (for response latencies and response accuracy) tended to favour the left hemisphere when the participants were tested during sleep deprivation.